with whom BETTY B. FLETCHER, PREGERSON, PAEZ and RAWLINSON, Circuit Judges, join in dissent.
The objective record embodied in the trial transcript plainly shows that Edwards’ counsel, John Meyers, never understood the California law of marital privilege. In granting the writ, the district judge, himself an experienced former California Superior Court judge, found that Meyers’ waiver of Edwards’ privilege was neither tactical nor reasonable. Nonetheless, the California Court of Appeal held that Meyers made the tactical decision to intentionally waive Edwards’ privilege rights. The majority reads the Court of Appeal’s decision as concluding that Meyers simply made a high-risk tactical decision to try to get into evidence one of Edwards’ conversations with his wife without opening the door to her damning account of his supposed confession to her. But even if the majority’s reading is accurate, tactics based on ignorance cannot be what Strickland contemplates as “sound trial strategy,” see Strickland v. Washington, 466 U.S. 668, 689, 104 S.Ct. 2052, 80 L.Ed.2d 674 (1984); rather it is the essence of attorney incompetence to fail to understand the governing law necessary to formulate such a strategy. The clear record evidence of incompetence here is “too powerful to conclude anything but” that Meyers mistakenly waived Edwards’ marital privilege. Miller-El v. Dretke, 545 *1130U.S. 231, 265, 125 S.Ct. 2317, 162 L.Ed.2d 196 (2005).1 Moreover, we cannot agree with the dire picture the majority paints to justify Meyers’ supposed strategy — that “desperate circumstances require desperate measures.” The district court carefully analyzed the trial record in concluding that the benefits of getting Edwards’ version of what he said to his wife, Kemet Gaines, about the anonymous caller were dwarfed by the risk of Gaines then being allowed to testify about her highly prejudicial version of the “dog mess” conversation.
We are mindful that AEDPA sets a high standard to allow us to find a state court’s application of law or factual determination to be “unreasonable,” see 28 U.S.C. § 2254(d); Rice v. Collins, 546 U.S. 333, 126 S.Ct. 969, 976, 163 L.Ed.2d 824 (2006), and that we must presume an attorney’s conduct involved a competent trial strategy, see Strickland, 466 U.S. at 689, 104 S.Ct. 2052. On this record, however, we conclude that Edwards clears both hurdles. Meyers lacked the legal competence to make such a decision. His inappropriate questions, misinformed legal arguments and the predictable damage resulting from opening the door to his wife’s version of their discussion are ample evidence of his incompetence. An attorney cannot make an informed tactical decision to waive a privilege he does not understand. Thus it was objectively unreasonable for the California Court of Appeal to find Meyers effective here. Because Edwards was prejudiced by his counsel’s deficient representation, we would affirm the district court’s grant of Edwards’ habeas petition. We therefore respectfully dissent.
I. Facts
The majority’s summary of the facts understates the extent to which Meyers lacked a basic understanding of the law of privilege and waiver, as evidenced by the trial transcript. Meyers failed to understand the law governing marital privilege, not just at the beginning of trial but throughout. He never shook his misper-ception that he could pick and choose parts of sensitive communications between Edwards and Gaines without waiving the privilege, even when warned by both the prosecutor and the trial judge. His misunderstanding led directly to his waiver of Edwards’ rights.
Meyers knew before trial that Edwards’ wife had told police that she was prepared to testify that during the exchange with Edwards on July 17 about why he was washing his hands, he had confessed to murdering Don Thomas. In anticipation of Gaines’ testimony, Meyers raised the issue of marital privilege, obtaining a trial court ruling in limine that Gaines could testify only about discussions between her and Edwards regarding the insurance fraud scheme, and about her observations of Edwards’ behavior on the nights in question.
Nonetheless, Meyers proceeded nearly to fumble away the benefit of this limiting order by asking Gaines what reason Edwards had' given for washing his hands on July 17, the night of the murder. Responding to an objection from the prosecution that Meyers was getting into privileged territory, Meyers asserted at sidebar that the conversation about Edwards’ washing his hands was “not a confidential communication.” Meyers argued that some conversations between Edwards and *1131Gaines were confidential, but others were not. Astonishingly, Meyers also argued that he could ask Gaines about communications with Edwards because she had waived her marital privilege by taking the stand. Meyers mistakenly believed that because Gaines was not asserting her marital privilege, he could ask her about confidential communications with Edwards without waiving Edwards’ privilege.
The trial judge attempted to clarify waiver law for Meyers, explaining that other than statements made in furtherance of the insurance fraud crime, “any statements that are made are ... confidential because they are between a husband and a wife.” Accord North v. Superior Court of Riverside County, 8 Cal.3d 301, 310, 104 Cal.Rptr. 833, 502 P.2d 1305 (Cal.1972) (holding that all statements made between husband and wife are presumed confidential). The court also informed Meyers that he could not “characterize certain conversations as [not] confidential because [Edwards and Gaines] might happen to be talking about the dog. They are still confidential.” Meyers responded, “That’s a pretty good issue,” and withdrew the question.
Despite the trial court’s lesson in evidence law, Meyers continued to blunder. During his direct examination of Edwards, Meyers asked about the evening of July 18 when Edwards received a death threat over the telephone from the victim’s cousin, Tyrone Melton. Specifically, Meyers asked Edwards whether he told Gaines anything about the phone call. Edwards responded, “I told her, ‘Somebody killed Don and they think I had something to do with it, and they just threatened to come and kill us.’ ” After another objection from the prosecution, the court told Meyers that he had allowed Edwards to waive the marital privilege by “testify[ing] to what [Edwards] told [Gaines].” Meyers objected, contending once again that “every statement made between a husband and wife is not a confidentiality privilege” and that Edwards had not waived the privilege because any communication between Edwards and Gaines regarding the phone call “wasn’t confidential.” When told by the court that Edwards could not “pick and choose” which conversations were confidential and which were not, Meyers replied, “Sure you can.” Obviously, the court’s prior explanation that all communications between husband and wife are presumed confidential had been lost on Meyers.
The court gave Meyers the opportunity to come in the next morning and provide some authorities for his proposition that Edwards could designate certain conversations confidential and others not confidential. Significantly, Meyers returned empty-handed, and was forced on the spot to read and respond to the key California case — People v. Worthington, 38 Cal.App.3d 359, 113 Cal.Rptr. 322 (1974)— which was new to him. Meyers’ extemporaneous riff on Worthington predictably did not persuade the judge, who ruled that Edwards’ marital privilege indeed had been waived. Meyers immediately responded, “Well, one thing for the record, that raises a significant [ineffective assistance of counsel] claim if he is convicted on appeal, in my judgment. ¶ [W]hat you’re saying is I erred in asking that question and I, quote, opened the door, close quote, to all the other stuff coming in. To me, that’s inadequate representation of counsel.” The trial court disagreed, finding that it was a “tactical decision,” although adding that “[m]aybe you didn’t anticipate it was breaching the privilege.... ” Meyers responded, “It wasn’t a tactic. It was a mistake.”2
*1132II. Discussion
A. Meyers Mistakenly Waived Edwards’ Privilege
The district court correctly rejected the California Court of Appeal’s finding that Meyers’ acts reflected “tactical” decisions. The Court of Appeal reasoned that:
In view of the strong evidence against appellant, defense counsel could reasonably have decided to introduce appellant’s testimony regarding his version of the conversation he had with Gaines on the night of July 17, 1991. In fact, as previously noted, the first jury deadlocked on the murder charge. Since defense counsel was aware that the trial court had ruled that defense counsel could not introduce evidence of the defense’s version of a conversation between appellant and Gaines without opening the door to the prosecution’s version of that conversation, the trial court reasonably determined that eliciting appellant’s testimony regarding his conversation with Gaines on the night of July 17, 1991, was a reasonable tactical decision rather than ineffective assistance of counsel.
(Emphasis added.)
In essence, the court assumed that Meyers deliberately decided to open the door to Gaines’ confession testimony, notwithstanding his earlier efforts to keep her testimony out and despite his articulated misunderstanding of the all-or-nothing character of the privilege. Such a high risk, self-destructive defense strategy seems implausible on its face. As borne out by the transcript, and by the obviously devastating impact on Edwards’ defense of letting Gaines testify that he had essentially admitted to having killed Don Thomas, the Court of Appeal’s reading of the record is not just implausible but objectively unreasonable.
The majority, which apparently does not want to defend the Court of Appeal’s decision as written, acknowledges that Meyers at least initially “appeared to misunderstand the marital privilege,” (Op. at 1127), but posits that Meyers — warned by the trial court that he could not ask about parts of Edwards’ conversations with his wife — then made the tactical decision to ask the questions that led Edwards to waive the marital privilege, perhaps hoping he could “get by” without actually opening the door to Gaines’ damaging testimony. (Op. at 1179.) The record simply does not bear out such a knowledgeable strategy. Rather it shows that Meyers persisted in thinking he could ask about one interchange between the husband and wife without opening up their broader communications about the events of July 1991. Even the trial judge in calling Meyers’ questioning “tactical” acknowledged, “Maybe you didn’t anticipate it was breaching the privilege.... ” That observation not only underscores Meyers’ legal incompetence, but it gives the lie to the notion that Meyers had deliberately decided to waive the privilege.3
*1133In short, Meyers made no tactical decision to reverse course and let the prosecution put on Gaines’ damaging confession testimony. He opened the door by mistake, plain and simple. The Court of Appeal’s conclusion that Meyers intended to waive his client’s privilege simply is not borne out by the record. Nor is the majority’s alternative explanation objectively reasonable. The only “tactical” decision Meyers made was to get in Edwards’ statement to Gaines about the anonymous caller’s threat, thinking he could limit it to that. A tactical decision with devastating consequences based on a mistake of law is not effective assistance of counsel.
B. Meyers’ Performance was Deficient
Even if the California Court of Appeal reasonably understood Meyers to have made a tactical decision to waive the privilege, the state court unreasonably applied the Strickland, standard in finding the tactic to be reasonable. By waiving Edwards’ marital privilege and exposing him to the devastating impact of a confession for little testimony of value in return, Meyers acted outside the bounds of professional competence. Indeed, the calculus was so one-sided as to reinforce the conclusion that Meyers acted out of ignorance.
In Strickland, the Supreme Court held that to prevail on an ineffective assistance claim, a petitioner “must show that counsel’s performance was deficient. This requires showing that counsel made errors so serious that counsel was not functioning as the ‘counsel’ guaranteed the defendant by the Sixth Amendment.” 466 U.S. at 687, 104 S.Ct. 2052. As the district court properly recognized, the Supreme Court and this circuit have compared the risks and benefits associated with a lawyer’s tactical decisions. See, e.g., Darden v. Wainwright, 477 U.S. 168, 186, 106 S.Ct. 2464, 91 L.Ed.2d 144 (1986); Mak v. Blodgett, 970 F.2d 614, 619 (9th Cir.1992). If we apply that kind of analysis to Meyers’ decision to waive the privilege, the ledger is decidedly one-sided against waiver. By waiving Edwards’ marital privilege, Meyers opened the door to testimony from Gaines. Meyers knew that Gaines was openly hostile to Edwards and had told police that he had confessed the murder to her. Not only did Gaines tell the police about his confession, but she told them that “he’s crazy,” she feared him and he had threatened her. Indeed, it was Gaines who, five years after the murder, tipped off the police that her husband was the murderer. Meyers knew that Gaines was firmly in the prosecution’s camp. Balanced against this near-certain and near-dispositive evidence, there was little for Edwards to gain from Gaines’ testimony.
The majority speculates that Meyers waived the privilege so that the jury would not be left to wonder whether Edwards attempted to explain his behavior — such as pacing the apartment with a shotgun and washing his hands — to his wife. (Op. at 1128.) But Edwards had already explained his behavior to the jury — without waiving the marital privilege — simply by testifying that Melton had threatened both him and his wife, and by describing his attempt to clean up his dog’s mess. The additional question of whether Edwards tried to explain those actions to his wife *1134concerns a minor detail that pales in importance to Gaines’ revelation of Edwards’ confession.
Similarly, the majority states that without waiver, “there was no innocent explanation for [Gaines’] decision to accompany him on their cross-country trek.” (Op. at 1128.) That assertion is perplexing; Edwards testified that Melton had threatened both Edwards and Gaines without waiving the privilege. Such testimony did not require delving into confidential communications between Edwards and Gaines and provided reason enough to explain why Gaines accompanied Edwards when he fled from the state. The only benefit Edwards could have hoped to receive from waiving the privilege was showing that Gaines knew she too had been threatened by the victim’s cousin. Once again, we are not persuaded that it was reasonable for Meyers to seek the minimal benefit accorded by this additional fact in exchange for the near-certain revelation of a murder confession.
Nor was Meyers’ waiver of Edwards’ privilege reasonable even assuming there was a non-frivolous argument that waiver should be limited to conversations that occurred on July 18, the night after Edwards confessed to his wife. (Op. at 1128-29.) That the scope of waiver was unsettled under California law at the time only bolsters my conviction that Meyers’ decision to waive was unreasonable. In light of the considerable risk posed by Gaines’ testimony, Meyers should not have plowed blindly into protected communications without first attempting to clarify the effect of waiver through a motion in limine.4
The majority excuses Meyers’ decision to waive the privilege by recalling the adage, “desperate times call for desperate measures.” (Op. at 1128.) As a preliminary matter, characterizing Edwards’ case as desperate is misleading. All of the evidence linking Edwards to the crime was circumstantial. Although the victim’s cousin, Tyrone Melton, testified that Edwards told him, “And I’ll fuck you up too,” Melton’s testimony was ambiguous and weak in comparison to what Gaines would have to say. On cross-examination, Melton’s credibility was undermined when he admitted that he personally desired to see Edwards convicted. The defense also brought out that when Melton signed a police statement less than two weeks after the murder, he recounted his phone conversation with Edwards and left out any reference to Edwards’ alleged self-incriminating statement. At that time — when the conversation with Edwards was freshest in his mind — Melton told the police only that Edwards had denied knowing about the murder of Thomas or who had committed it.
Moreover, the majority’s “desperate times” thesis does not excuse ineffective assistance of counsel. As Strickland established, even in desperate times, there are discernible limits on counsel’s justification for taking unwarranted risks. The decision to waive Edwards’ marital privilege falls outside those limits. When the ultimate balance is calculated, the cost of waiving Edwards’ marital privilege overwhelmingly out-weighs any benefit to Edwards. By waiving Edwards’ marital privilege rights, Meyers provided ineffective assistance and the California Court of Appeal was objectively unreasonable in finding otherwise.
*1135C. Edwards was Prejudiced by Meyers’ Ineffective Assistance
To prevail on a claim of ineffective assistance, Edwards must also show “that there is a reasonable probability that, but for counsel’s unprofessional errors, the result of the proceeding would have been different. A reasonable probability is a probability sufficient to undermine confidence in the outcome.” Strickland, 466 U.S. at 694, 104 S.Ct. 2052. The second trial judge explicitly found that Edwards was prejudiced by the waiver of his marital privilege, stating that without Gaines’ testimony:
the verdict may well have been a different one. So that I want to make it clear that if I’m wrong on this, I do think it’s reversible, from my standpoint, for whatever the court of appeals wants to decide because this is a key issue in this case. This testimony was very damaging.
The trial court’s unequivocal assessment of prejudice is entitled to deference under 28 U.S.C. § 2254(d) and was not objectively unreasonable.
When a state trial court reaches a reasoned conclusion that the appellate court subsequently does not address, traditionally we have treated the trial court’s determination as the last reasoned decision. See Hirschfield v. Payne, 420 F.3d 922, 928 (9th Cir.2005) (reviewing trial judge’s oral decision to deny petitioner’s motion to represent himself because state appellate court did not address the ruling). The trial court’s finding is the only determination on prejudice in the entire state court record. Affording the state trial court’s determination adequate deference under AEDPA, we cannot say that its finding of prejudice was objectively unreasonable. Without the confession, the only evidence linking Edwards to the crime was circumstantial and the impeached testimony from the victim’s cousin that Edwards threatened to “fuck you up too.” A defendant’s own confession is the most damning sort of evidence available against him. See Bruton v. United States, 391 U.S. 123, 139-40, 88 S.Ct. 1620, 20 L.Ed.2d 476 (1968) (“[T]he defendant’s own confession is probably the most probative and damaging evidence that can be admitted against him.”). Because a confession is so damaging, we are persuaded that under the circumstances, the trial judge reasonably concluded that Edwards was prejudiced by the waiver of his marital privilege.
III. Conclusion
The California Court of Appeal’s conclusion that Meyers made a tactical decision to waive Edwards’ marital privilege was objectively unreasonable; the trial transcript makes clear that Meyers did not comprehend the basic legal underpinnings of the law of privilege and waiver and waived Edwards’ rights only in error. Moreover, by opening Edwards up to the most damning evidence available for little in return, Meyers rendered ineffective assistance of counsel. The state trial court’s finding that there was a reasonable probability that but for Meyers’ ineffective assistance, the verdict would have been different was reasonable. We would affirm the district court and grant the habeas petition. We therefore respectfully dissent.
. See Edwards v. Lamarque, 439 F.3d 504 (9th Cir.2005), vacated, 455 F.3d 973 (9th Cir. 2006).
. We agree with the majority that Meyers' mea culpa claiming mistake is not dispositive. (Op. at 1126-27.)
. Like the majority, we recognize that the trial judge "had observed Meyers throughout the trial." (Op. at 1127.) However, given the judge’s seemingly contradictory conclusion that Meyers waived Edwards' rights as a litigation tactic but may not have known he was doing so, his "tactical" finding should carry less weight, notwithstanding the deference we owe the trial judge and the limitations of appellate review from a trial transcript. Cf. Rice v. Collins, 546 U.S. 333, 126 S.Ct. 969, 975-76, 163 L.Ed.2d 824 (2006) (reviewing credibility findings of state trial court); see also id. at 977 (Breyer, J., concurring) (reminding that "[t]he trial judge is best placed *1133to consider the factors that underlie credibility” and that "[ajppellate judges cannot on the basis of a cold record easily second-guess a trial judge’s decision about likely motivation” when reviewing Batson challenges). The trial judge did not articulate any reasoning that is not captured by the trial transcript — Meyers’ demeanor, for example — but rather the judge appears to have accepted, as the majority now does, that it is constitutionally acceptable for an attorney to make a strategic decision based on an erroneous understanding of the law.
. Meyers did not seek a preliminary ruling on the consequences of Edwards testifying about his version of conversations with Gaines or the limits of the testimony he could elicit from Gaines.