Acting White House chief of staff Mick Mulvaney said on Fox News Sunday that Democrats will never get their hands on President Trump's tax returns, adding that the request is "a political stunt" that the IRS will not comply with.

"That’s an issue that was already litigated during the election. Voters knew the president could have given his tax returns. They knew that he didn’t and they elected him anyway."

The big picture: Though he at one point said during the 2016 campaign that he would be releasing his tax returns "shortly," Trump has walked back the promise and claimed he is unable to do so because he is under IRS audit. House Ways and Means Chairman Richard Neal (D-Mass.) last week formally requested Trump's tax returns using an obscure IRS code that gives him the power to request tax documents from anyone — potentially triggering an extended legal battle that could make its way to the Supreme Court.

Go deeper: The 2020 candidates who have released their latest tax returns