President-elect Donald Trump opposes probing whether Russia meddled in the 2016 election. He triggered a risky conflict with China over the status of Taiwan. He chose Gary Cohn, president of Goldman Sachs, to lead the National Economic Council, and Steven Mnuchin, a Goldman Sachs partner, as treasury secretary. Were these high-stakes decisions made to benefit the public’s interests ... or his own?

Citizens cannot properly evaluate that proposition, to know whether Trump is advocating on behalf of America or acting to safeguard his family’s global business holdings, because the president-elect still refuses to release his tax returns.

This aberrant reality is losing impact because it is old news. Yet it matters more each day, and will matter most when Trump becomes the most powerful person on earth.

As Mitt Romney once put it, “Tax returns provide the public with its sole confirmation of the veracity of a candidate's representations regarding charities, priorities, wealth, tax conformance, and conflicts of interest. Further, while not a likely circumstance, the potential for hidden inappropriate associations with foreign entities, criminal organizations, or other unsavory groups is simply too great a risk to ignore.”

Richard Painter and Norman Eisen, who advised Presidents George W. Bush and Barack Obama on ethics, agree:

Trump says his tax returns reveal nothing that is not already disclosed on his official candidate financial disclosure, called Form 278e. As ethics counsels to the past two presidents, we dealt with both their tax filings and their Form 278's and so we know that Trump is wrong. His tax filings have an enormous amount of additional information which, in this case, could be critically important to determining whether his business overseas might affect his decision-making as president. That is because Trump’s 12,000-page tax return may tell us a great deal about his Russian and other foreign business ties that is not on his 104-page campaign financial disclosure.

Voters want to see Trump’s taxes, too.

“74 percent of all likely voters wanted to see his returns, and 62 percent of Republicans said the same thing,” the New York Times notes. Yet they remain submerged in a swamp of conflicting interests more fraught than any in the modern era.

Last month, after some of Trump’s worrying foreign conflicts were exposed, I argued that Congress cannot fulfill its constitutional duty to check and balance the next president, or provide adequate oversight of the federal agencies he presides over, without a full, accurate understanding of his business holdings and debts. I urged Americans to tell their representatives that they favor an exhaustive inquiry into Trump’s finances to determine exactly where his interests and ours diverge.

Inevitably, public attention turned to other matters.

The president-elect kept tweeting to his advantage. He kept naming political appointees. He continued to decline many of the intelligence briefings available to him. Whether on foreign policy, the fate of Obamacare, abortion politics, the Supreme Court, or any number of other issues, he kept observers guessing about what is next.

But significant focus should remain on his finances, and the need to expose them to sunlight, because so many of the wildly divergent questions he’ll tackle as president, especially in the realm of foreign affairs, could dramatically affect his family’s wealth. And while that wealth may be as stable as the president-elect would have us believe, it is also possible that Trump’s solvency is more tenuous than many imagine, that he will be forced to act unethically for his family business to survive.

Congressional Republicans should insist on learning if that is so.

And in theory, they see the value in sunlight. House Speaker Paul Ryan, who released his tax returns while running alongside Mitt Romney in 2012, said during the 2016 campaign that Trump should release his tax returns. House Oversight Chairman Jason Chaffetz did, too. Representative Mark Sanford, a South Carolina Republican, penned an op-ed urging Trump to come clean. “There is a reason a banker wants to see tax returns in determining whether you are eligible for a mortgage,” he wrote. “You may talk a good game; tax returns don’t. Mr. Trump knows this, which is why his team had Gov. Pence of Indiana disclose his tax returns.”

Primary rivals Ted Cruz and Marco Rubio urged Trump to release his tax returns, too. Even Kellyanne Conway and Roger Stone have said that they’d like to see the documents!

Those Republicans all commented during the campaign.

Now, the failure to reveal conflicts of interest doesn’t just affect the horse race in an election, it concerns knowing whether Trump will look after the national interest and whether his overseers will know the difference. Republicans ought to care more about seeing Trump’s tax returns now than they ever did before, if their primary motivation really is the welfare of the country. Yet many are ignoring the matter.

This despite the dangers it poses.

Trump lost the popular vote by a wide margin. Some presidential electors are having crises of conscience about whether to vote for him. In an election in which there are plausible though unproven allegations of foreign interference, Trump is on record stating, in a campaign news conference in Florida, “I will tell you this, Russia: If you’re listening, I hope you’re able to find the 30,000 emails that are missing.” And he won while promising supporters that he would “drain the swamp.”

For all those reasons, even the appearance that Trump is selling out America to bolster foreign interests could one day spark a crisis of legitimacy that would be best avoided.

The country would be best-served if Trump ends the speculation into his conflicts of interest himself. If he refuses, Congress has an urgent duty to aggressively probe this matter. Insofar as individual Republicans refuse to sign on, they should be forced to explain why they’re comfortable remaining in ignorance of Trump’s incentives. Just imagine what they would insist on if Hillary Clinton were behaving the same way.