Jonathan Ernst / Reuters

President Donald Trump has defied a congressional subpoena and refused to deliver his tax returns as the law requires. The headlines say that the decision is Secretary of the Treasury Steven Mnuchin’s, but that, of course, is a fiction. Mnuchin’s statement insists that he acted on the advice of the Department of Justice. But the law and the precedents are clear: Congressional subpoenas must be complied with, and neither the president nor the courts have any authority to judge which subpoenas “serve a legitimate legislative purpose” and which do not. Congress is its own judge in these matters, as the Supreme Court affirmed in 1975 in the classic case on the topic.

Most analysts explain Trump’s actions as a play for time. He may ultimately lose—but if that ultimately can be postponed past November 2020, a late loss may serve as the next best thing to a win.

But here’s a reason to wonder whether the calendar serves Trump quite as well as most analysts assume. What is Trump hiding in those returns? Your guess is as good as anyone’s. The secret could be mild: He’s not as wealthy as he likes to boast. The secret could be embarrassing, but not illegal: He personally hugely benefited from special favors in the recent tax cut. The secret could raise national-security concerns. Or the secret could even point to a lifelong career of financial fraud.

The longer the fight over the returns continues—especially if Trump loses in the lower courts but appeals and appeals again—the more likely it is that Americans will assume the worst.

Trump already suffers from a wide and deep public-opinion disbelief in his integrity. In September, Gallup asked respondents to rate Trump’s ethics compared with those of other presidents. Sixty-eight percent regarded him as less ethical than Ronald Reagan; 58 percent as less ethical than Barack Obama; and 52 percent as less ethical than Bill Clinton.

Trump even suffers in comparison to Richard Nixon: 43 percent rate Trump as less ethical than Nixon, while only 37 percent rate him higher.

Quinnipiac University produced even more troubling results in March. Sixty-five percent told pollsters that they regard Trump as dishonest, the worst honesty number yet recorded by any survey. Sixty-four percent of Americans believe that Trump committed crimes before becoming president.

It’s often assumed that Trump has a solid 40 percent base. But that’s not true on ethics matters. Ethics surveys reveal a split between strong supporters and softer supporters.

When the Pew Research Center asked in January whether Trump was separating his business interests from his official duties, only 28 percent expressed strong confidence that he was doing so. Another 13 percent described themselves as “somewhat” confident. While 66 percent of conservative Republicans expressed strong confidence in Trump’s integrity, only 39 percent of self-described moderate Republicans did so.

It’s unrealistic to imagine a split within the GOP over these issues, but it’s easy to imagine a continued melting away of Trump’s support on questions of ethics. Nearly two-thirds of Americans now agree that Trump should release his tax returns, again according to Pew.

Polls will not bend Trump on an issue as seemingly existential to him as keeping his tax returns concealed. But the issue of the tax returns may bend Trump’s polls.

Over the next weeks, Trump will be fighting multiple financial-disclosure fights. He has intervened to stop Deutsche Bank from complying with a congressional subpoena of his bank records. He threatens to fight to prevent Special Counsel Robert Mueller from testifying about Trump’s Russia connections. He’s already lost the first round of the emoluments-clause lawsuit filed by the state of Maryland and the District of Columbia.

As Trump fights to conceal his financial records, loses, appeals, and loses again, it becomes progressively more plausible to Republicans that those records conceal damaging revelations about serious wrongdoing. Trump is ultimately fighting to prove he’s not a crook. He can postpone delivering the records that would prove the matter one way or another. But as he fights to postpone the inevitable, he risks convincing voters that they do not need a subpoena to read his guilt.

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