Sen. James Lankford (R-Okla.) thinks President Donald Trump ought to release his income tax returns.

“He promised he would,” Lankford said at a town hall in Oklahoma on Tuesday. “He should keep his promise.”

Trump has long maintained that he can’t do so because he is being audited by the Internal Revenue Service. “It’s a routine one. It continues,” White House Press Secretary Sean Spicer said Monday.

The IRS, however, has said that nothing prevents individuals from sharing their tax information even while under audit. Moreover, there is a precedent for a president releasing tax returns while under audit ― Richard Nixon did so.

Asked Monday whether Trump would authorize the IRS to confirm the existence of the audit he has repeatedly cited, Spicer demurred.

“We’re under the same audit that existed, and so nothing has changed,” he said.

While most Democrats have called on Trump to release his tax returns, few Republicans have joined them.

“As far as I’m aware, the president says he’s still under audit,” Sen. Tom Cotton (R-Ark.) said at a town hall in Arkansas on Monday, prompting boos from the audience.

Republicans who have broken with their party and called on the president to release his tax returns include: Sen. Joni Ernst (R-Iowa), Rep. Mark Sanford (R-S.C.), Rep. Ted Yoho (R-Fla.), Rep. Justin Amash (R-Mich.), Rep. Walter Jones (R-N.C.), and Rep. Matt Gaetz (R-Fla.).

Over the weekend, in honor of Tax Day, thousands of Americans took to the streets, demanding Trump release his tax returns. More than 1 million people have signed a White House petition calling on him to disclose the information.

The president responded on Twitter.

I did what was an almost an impossible thing to do for a Republican-easily won the Electoral College! Now Tax Returns are brought up again? — Donald J. Trump (@realDonaldTrump) April 16, 2017