IN A 28-day tenure already marred by many blunders — both by his staff and by himself — President Trump’s rambling news conference Thursday, riddled with misstatements of fact and attacks on reporters, stands out mainly for its consistency with what came before. It was seemingly meant to counteract growing concerns, including among Republicans on Capitol Hill, that the ouster of a national security adviser for lying to the vice president was indicative of administration competence generally, or of a sinister association with the regime of Vladi­mir Putin. If so, Mr. Trump’s stream-of-consciousness performance — “I’m not ranting and raving,” he said at one point — may not have done the trick.

At several key moments, Mr. Trump dismissed questions about any connections he and his circle may have had with Russia. “The whole Russian thing, that’s a ruse,” he declared. News reports suggesting that some of his associates had contact with Russian officials during the election were “fake,” he insisted — even as he condemned the leakers who released classified information to the media. The bottom line, according to the president, is this: “I own nothing in Russia. I have no loans in Russia. I don’t have any deals in Russia.”

This would be good news, and it may well be true. If only the public could trust it.

Mr. Trump ran as the least transparent major-party candidate in modern U.S. history, and he has done little since his victory in November to change that. Bucking decades of practice, he refused to release his tax returns, after promising he would do so. His excuses did not wash. Though his recent returns may be under audit, nothing is stopping him from releasing the documents he swore were true when he sent them to the Internal Revenue Service. There is certainly nothing preventing him from releasing returns from earlier years. If Mr. Trump wants Americans to take his assurances about his international business arrangements seriously, releasing his tax information is the starting point.

It may be that, as Mr. Trump has indicated in the past, his tax returns would not shed as much light on his business entanglements as some have suggested. In fact, that is an argument for even more transparency, not less. Mr. Trump was a unique presidential candidate in the potential scale and scope of his international conflicts of interest. That demanded an unusual level of disclosure — thorough and complete accounts of how he conducted his business affairs, which he claimed as his central qualification for the presidency, and his positions heading into the White House.

Though Mr. Trump announced some worthwhile steps to separate himself from his business empire, they are significantly less valuable if the public does not know what his exposure was before he signed away operations to his sons. We should know what sorts of assets he has in what places, to whom he owes money and at which governments’ pleasure his businesses operate.

Throughout Mr. Trump’s sprawling news conference, as he spoke about Russia, the “mess” the country is in, media “dishonesty,” Democrats’ errors and a variety of other issues, this point rang true: It would be a lot easier to give the president the benefit of the doubt if he backed his words with evidence.