Trump says no one cares about his tax returns anymore. This GOP congressman does.

FILE - In this Dec. 18, 2013, file photo, U.S. Rep. Mark Sanford, R-S.C., discusses his first months back in Congress during an interview in Mount Pleasant, S.C.
FILE - In this Dec. 18, 2013, file photo, U.S. Rep. Mark Sanford, R-S.C., discusses his first months back in Congress during an interview in Mount Pleasant, S.C. AP

President-elect Donald Trump shrugged off questions about his unreleased tax returns on Wednesday, arguing that Americans aren’t concerned about the issue.

“I won. And became president,” he said at a press conference, the first one in nearly six months. “You know the only ones who care about my tax returns are reporters.”

Rep. Mark Sanford says he cares, too.

You know, the only one that cares about my tax returns are the reporters, OK? They're the only ones.

President-elect Donald Trump

“I think it’s a grave mistake for President-elect Trump to assume that no one - except reporters - cares about whether or not he releases his tax returns,” the South Carolina Republican said in a statement on Wednesday. “I care...If President-elect Trump wants us to take him at his word, then certainly he should hold true to his former promises to make his tax returns public.”

During his campaign, Trump insisted that he could not release his tax returns because they were under audit. The Internal Revenue Service told McClatchy last year that there is nothing preventing Trump from releasing his tax information, whether he is being audited or not.

[READ MORE: Trump says he ‘can’t’ release his tax returns. The IRS doesn’t see why not.]

This is not the first time Sanford has pressed Trump to release his taxes.

“To him, demands that he release his tax returns are just a ploy by his opponents and enemies to undermine his campaign,” he wrote about then-candidate Donald Trump in a New York Times op-ed, after Hillary Clinton released her taxes in August. “But that obstinacy will have consequences.”

As he did during his campaign, Trump on Wednesday insisted that “you don’t learn anything from a tax return.” In the weeks leading up to his inauguration he has been under pressure to prove that he doesn’t have financial or business ties to Russia that could be used as leverage against him, something his tax returns could shed light on.

The issue gained new urgency after CNN reported on Tuesday that U.S. intelligence agencies had presented Trump with allegations that Russia had compromising personal and financial information about him.

Trump’s refusal to release his taxes “will echo into future campaigns,” Sanford said on Wednesday. He has co-sponsored the bipartisan Presidential Tax Transparency Act, which requires major party candidates running for president to release at least three previous years of federal tax returns.

“This is not about invading (Trump’s) privacy or looking for avenues into opposition research, this is about upholding precedent and encouraging transparency,” he said, adding that he predicts a “trickle-down” effect will result in down-ballot candidates being let off the hook when it comes to being transparent about their finances.

Since President Gerald Ford, 19 of 20 major-party presidential candidates have released at least a year of tax returns.

Vera Bergengruen: 202-383-6036, @verambergen