The top Senate Democrat on Tuesday joined calls for President Donald Trump to release his tax returns, warning that a failure to do so could sink what was a major campaign promise.

Should the president opt to continue keeping his full personal financial picture secret, it would make any package of tax code changes and rate cuts “much harder to pass,” said Minority Leader Charles E. Schumer, D-N.Y.

Keeping his tax returns under wraps would cause lawmakers to “jump to the conclusion that he’s benefiting” from whatever the White House might insist be included in the measure, “and that’s why he’s doing it,” Schumer said on a conference call with reporters.

Schumer joins Democrats like Sen. Elizabeth Warren of Massachusetts in calling for the presidential release — but also more than 12 Republicans. That list includes Sen. Joni Ernst of Iowa, Rep. Mark Sanford of South Carolina and House Appropriations Chairman Rodney Frelinghuysen of New Jersey.

The White House on Monday signaled Trump has no plans to release his 2016 returns or any others.

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“He is still under audit, the statement still stands,” Press Secretary Sean Spicer said during his daily press briefing. He called the alleged audit “routine” and “one that continues.”

When pressed on why the president will not just say plainly that he will never release his financial documents, his top spokesman responded: “We’ll have to get back to you on that.”

Asked about talks to hammer out a measure to keep the government funded beyond April 28, Schumer told reporters talks are going “so far, so good.” He called for the White House to mostly stay out of ongoing talks, saying he is leery administration officials would insist on “poison pill” riders to which Democrats would object, leaving the measure shy of the votes to avert a federal shutdown in 10 days.