The president has insisted that testing in the U.S. is "much bigger and better" than other countries.
Mulvaney also said that the "deep state" is still trying to hinder Trump and expressed frustration that the president could not fire more obstructive officials.
President Donald Trump is no stranger to appearing on the big screen—and his impeachment trial playing out in the Senate is no exception.
"I think we ought to go through the right process," the lawmaker from Florida said.
Congressman Hakeem Jeffries, a House manager, pointed out that the Senate has conducted fifteen impeachment trials and there were witnesses at every single one.
The president was playing golf with professional John Daly while officials were trying to set up a call to have the aid released, according to The New York Times.
"Whether it's Mulvaney, Bolton, Giuliani, Pompeo—if they have to testify under oath, he has to leave," former White House Communications Director Anthony Scaramucci said on MSNBC.
The House is expected to impeach the president in a vote on Wednesday, and Senate leaders are now wrangling to decide the format of the subsequent trial.
Senator Chuck Schumer says he expects "some" of his Republican colleagues to say "that's fair," when they read his letter.
A representative for Republicans for the Rule of Law told Newsweek that the group targeted representatives who have shown a willingness to "assert their independence" of the president.
"It goes to a phrase we've all become familiar with in recent months, the idea of consciousness of guilt," Niall Stanage said.
Republican analyst Amanda Carpenter said she believes supporters of President Donald Trump could be planning to make acting White House Chief of Staff Mick Mulvaney the scapegoat for allegations levied at the president during the impeachment inquiry.
The close adviser to acting White House Chief of Staff Mick Mulvaney joins a number of other White House officials who have been instructed by the White House not to comply.
CNN host Victor Blackwell abruptly ended a Saturday panel about GOP impeachment strategies after a Republican harped on "debunked conspiracies" about Joe Biden and Hillary Clinton.
Ted Lieu, a Democratic congressman from California, has written a letter to White House Acting Chief of Staff Mick Mulvaney questioning a large exodus of cybersecurity staff.
The acting White House chief of staff is at risk of losing his job following a series of gaffes, with counselor Kellyanne Conway or Treasury Secretary Steven Mnuchin floated as possible replacements.
"I don't recall any conversations with the president about that phone call," the Republican Senate majority leader said.
"Very troubling," Representative Adam Levin told reporters outside the closed-door session.
"These [Republican] members are in a situation where they just can't defend the indefensible," former Representative Charlie Dent said.
"He's a good guy," Anthony Scaramucci argued, but said Mulvaney is "working for a terrible person."
The president was forced to U-turn over his plan to host the G7 Summit at one of his own properties.
"I think it's terrible. I don't agree with any of it," Francis Rooney said. "But they're derogating the work of our paid foreign service."
"You had talked about investigating the Democrats was part of the quid pro quo," Chris Wallace pointed out.
Joe Scarborough said: "There's no place to run. There's no place to hide, baby. It's all on video, and Mulvaney yesterday did more to move the president toward impeachment than anybody has over the past, well, three years."
Mick Mulvaney told reporters yesterday that the Trump administration uses quid pro quo "all the time with foreign policy." He later walked back the comments.
"So let's follow up with those Republican members who went on the tv and said there was no quid pro quo now that Mulvaney has enthusiastically admitted to it," Senator Brian Schatz tweeted.
"I have news for everybody: Get over it," Mulvaney told reporters on Thursday.
"The deficit under Obama dropped by an average of 11 percent a year in his second term," Chris Wallace told Mick Mulvaney.
"I think you're spending way too much time reading between the lines," Mulvaney said, when confronted with Trump's habit of using vermin metaphors to describe political foes.
Mulvaney said: "I don't particularly like Donald Trump as a person. But I am still voting for him."