Republican presidential nominee Donald Trump. (Evan Vucci/AP)

Democrats might take their push to force GOP presidential nominee Donald Trump to disclose his recent tax returns to the Senate floor next month, potentially complicating congressional efforts to address the Zika virus and fund the government past Sept. 30.

Sens. Ron Wyden (Ore.) and Chris Murphy (Conn.) told reporters Thursday that they would press for consideration of Wyden’s bill requiring major-party presidential nominees to disclose at least three years of tax returns. The bill, if passed, would allow the Treasury Department to release Trump’s returns over the objections of the New York businessman, who has cited an ongoing Internal Revenue Service audit as his reason for breaking with a 40-year tradition of disclosure by presidential candidates.

“The American people have just come to expect that tax returns would be released,” Murphy said Thursday. “This an exceptional moment where a long-standing precedent has been broken, and it presents enormous peril to the public to have this information as private.”

Wyden and Murphy said Trump could potentially act as president to benefit his investments abroad, including in Russia. They also raised questions about his charitable giving and whether he has withheld income or payroll taxes for personal employees — an issue that has tripped up several high-profile executive nominees.

Wyden said that voters “have a right to have that out in the open.”

Trump’s Democratic rival, Hillary Clinton, has released her past nine annual income tax returns. The disclosure of tax returns by presidential candidates — and by sitting presidents — has been a matter of latter-day political norms, not law, and Democrats have characterized Trump’s thumbing his nose at the tradition as outrageous.

In the summer of 2012, Democrats engaged in a similar effort to raise questions about GOP nominee Mitt Romney’s taxes, with then-Senate Majority Leader Harry M. Reid (D-Nev.) suggesting in early August that Romney paid no taxes.

Romney released his taxes in late September, showing that he did in fact pay taxes, though at a lower rate than most working Americans because his $13.7 million of 2011 income was largely from investments.

The Trump campaign did not immediately respond to an email seeking comment. Trump initially cited an ongoing audit for refusing to disclose his returns; there is no prohibition on releasing a return that is under audit, and Trump has since cited legal advice and his own privacy for not releasing them. His campaign released a letter from Trump tax lawyer saying his returns “have been under continuous examination by the Internal Revenue Service since 2002, consistent with the IRS’s practice for large and complex businesses.”

Trump has disclosed his tax returns in the past to casino regulators. The Washington Post and other news organizations have reported that Trump did not report any tax liability after taking advantage of provisions commonly employed by real estate developers.

Wyden, the senior Democrat on the tax-writing Senate Finance Committee, pointed out Thursday that it is unlikely that Trump’s 2015 return would be under audit already. Trump has filed a financial disclosure statement similar to the ones that members of Congress and other federal officials file on an annual basis. But tax returns would give fuller and more precise insight into his income and assets.

Asked whether legislators like himself should also be required to publicly disclose their returns, Wyden said he would be open to it but said the presidency is “too important to gamble with.”

“What we’re talking about is essential because we have a candidate who is flouting a 40-year tradition,” he said. “Since Watergate, every single Democrat, every single Republican has said this is something the American people have a right to have before they vote for the most important office in the world.”

Wyden’s bill, the Presidential Tax Transparency Act, gives a major-party presidential nominee 15 days to release their three most recent tax returns. After that, the Federal Election Commission would be empowered to request those returns from the Treasury Department and post them publicly.

Wyden said Democrats would “do everything we can to bring this bill up immediately as soon as we get back,” he said. The Republican Senate majority leader, Mitch McConnell (Ky.), controls the Senate floor, however, and there is little indication it will be taken up. McConnell spokesman Don Stewart declined to comment on what he called a “political messaging” bill.

The bill has been referred to the sleepy Rules and Administration Committee, though Democrats have tools available to force action on it — including by attaching it as an amendment to a must-pass bill.

Congress will meet for four weeks after Labor Day before adjourning again for the October campaign period. They must pass spending legislation to keep the government open past Sept. 30, when the federal fiscal year ends. If Democrats try attaching the presidential tax provision, it could complicate that effort.

Wyden said he would first seek a consensus path toward a vote on his bill, but he did not rule out more aggressive maneuvers to secure a vote on his bill.

“This is going to be a decision moment for Republicans,” Murphy said.