Treasury Department would not release Mr. Trump's tax returns to House Ways and Means Committee Chairman Richard Neal. Neal, citing a statute that gives the chairman of House Ways and Means the authority to obtain any individual's tax return, had demanded six years of Mr. Trump's taxes.

Mulvaney called efforts to obtain the tax returns "a pure show pony-type of situation," and said that House Democrats were just trying to "embarrass" the president.

"What's embarrassing about his tax records?" Garrett pressed Mulvaney.

"That's what they want to know," Mulvaney said, adding that he didn't know if there was any embarrassing information in Mr. Trump's returns because he had not seen them.

"I don't care, and more importantly, voters don't care. Keep in mind, everybody knew, everybody who cared knew that the presidentdidn't produce his tax records before the election, and they voted for him anyway," Mulvaney continued. "So from a political perspective, this debate is over. The Democrats are trying to continue that political conversation and there's no reason to do it."

Trump Jr. subpoena

Mulvaney also addressed other pressing issues, like the Senate Intelligence Committee's subpoena of Donald Trump Jr. The committee is chaired by Republican Sen. Richard Burr.

For the Senate Intelligence Committee to subpoena Mr. Trump's son and "not at least get a heads-up, I thought was -- let's say bad form," Mulvaney said. He said he did not know whether the president was also caught by surprise.

Mueller report

Mulvaney said that Congress is also "not entitled to see" the full report by special counsel Robert Mueller, countering Democrats' argument