Vice President Pence took center stage on Sunday morning’s news shows, embracing his role as President Trump’s most ardent and unflinching supporter amid mounting outrage from Democrats over Trump’s call for the Justice Department to investigate an op-ed describing a “resistance” movement within his administration.

In interviews on “Fox News Sunday” and CBS’s “Face the Nation,” Pence not only said that he would take a lie-detector test to prove that he hadn’t written the anonymous New York Times piece but that he would do so “in a heartbeat.” He disputed the veracity of an episode in Bob Woodward’s new book depicting a White House in chaos, even when confronted with a document backing up the veteran journalist’s reporting.

And in an unusual move, he requested an opportunity to go back on camera and revise his response to a question on whether anyone on his staff had written the op-ed, telling CBS’s Margaret Brennan that he was “100 percent confident” no one on his team was involved after earlier ­responding that he “just wouldn’t know.”

Pence’s remarks in the back-to-back interviews highlighted his eagerness to serve as Trump’s most loyal defender, a role that has defined his time as vice president and one that has earned him praise from the president’s supporters but scorn from critics who contend his defense and promotion of Trump is over the top.

“Especially at a time when you have a besieged president, you can expect the vice president to be supportive,” said Tim Naftali, a presidential historian at New York University and the founding director of the Richard Nixon Presidential Library and Museum. “What makes Vice President Pence unusual is that he is repeating Trumpian exaggerations and Trumpian lies.”

He added: “Does the vice president’s loyalty to this administration have to extend to servility?”

The appearances by Pence come as Trump has called on the Justice Department to investigate the author of the New York Times piece, which described a “two-track presidency” in which some senior aides are actively working to thwart Trump’s “misguided impulses” and have even discussed removing the president from office via the 25th Amendment.

They also come as former president Barack Obama has stepped forward to harshly criticize Trump and Republican politics, comparing Trump in a speech Friday to demagogues around the world who exploit “a politics of fear and resentment and retrenchment.”

Pence has previously drawn attention — and, at times, mockery — for his enthusiastic support of Trump. He frequently remarked on Trump’s “broad-shouldered” leadership during the 2016 campaign and last year raised eyebrows when he praised the president for nearly three minutes straight at a Cabinet meeting.

On Sunday, he again lauded Trump personally, describing him in the CBS interview as “the most accomplished president of my lifetime and, I think, already one of the most successful presidents in American history in our first two years.”

But he took things one step further with his sharp denunciation of the op-ed and Woodward’s new book, “Fear.”

Some have pointed to the use of the word “lodestar” in the op-ed as a sign that it may have been penned by Pence, who has used the word frequently in speeches. The vice president has vigorously denied that he was the author, but that has not discouraged House Minority Leader Nancy Pelosi (D-Calif.), who has speculated openly about Pence and floated his name once again in a Sunday tweet.

Pence declined to say whether he believed someone had purposely inserted the word into the piece to set him up, telling Fox News Channel’s Chris Wallace, “I wouldn’t know.” He called the op-ed “a disgrace” and said he would gladly submit to a lie-detector test to prove that he did not write it.

“I would agree to take it in a heartbeat and would submit to any review the administration wanted to do,” Pence said.

Whether lie detectors will be employed or not, Pence was wise to use such strong imagery at a time of tumult in the White House, said Republican strategist Doug Heye.

“Everyone in this administration communicates with the president through TV, no matter however else they communicate with him. The president responds to what he sees on TV, and he responds to imagery,” Heye said.

Pence also said it was “very disappointing” to see Obama “break with the tradition of former presidents and become so political” in his attacks on Trump in his Friday speech. He disputed one of the episodes reported by Woodward in his book, in which the journalist writes that Trump economic adviser Gary Cohn removed a document from the president’s desk in September 2017 to stop him from signing it.

“I have every doubt that that happened,” Pence told Wallace. He continued to suggest that the incident never occurred, even after Wallace held up for Pence a copy of the document, which would have terminated the free-trade deal with South Korea.

In the CBS interview, Pence denied ever participating in any discussions with other Cabinet members about removing Trump from office.

Asked whether anyone on his own staff had anything to do with the New York Times op-ed, Pence initially said, “I wouldn’t know. And I really would hope not.”

But after the interview had concluded, according to CBS, Pence said he had misunderstood the question and asked for a chance to clarify his remarks.

“I thought you were speaking about the administration staff,” Pence told Brennan. “Let me be very clear, I’m 100 percent confident that no one on the vice president’s staff was involved in this anonymous editorial.”

He did not offer a direct answer when asked whether he had asked his staff, saying only, “I don’t have to ask them because I know them.”

Pence’s office confirmed CBS’s account of events and said that the vice president appreciated Brennan giving him the opportunity to append his remarks.

“He thought she was referencing administration-wide appointees, so he clarified,” a person in Pence’s office familiar with the situation said.

Heye said the follow-up exchange made it clear that Pence felt he needed to strengthen his language.

“I think whether you’re talking about a vice president or a Cabinet member or so forth, I don’t think it’s enough to say, ‘I don’t know.’ You do need to go that extra mile,” Heye said.

In recent days, Trump has said that he believes Attorney General Jeff Sessions should launch an investigation to identify the op-ed’s author, citing national security concerns.

Pence declined to say what, if any, law the author of the piece might have broken but maintained in his interview on “Fox News Sunday” that Trump’s “concern is that this individual may have responsibilities in the area of national security.”

Some Democrats on Sunday struck back at that argument, contending the op-ed and Trump’s response to it are proof that the president is not fit to serve.

“Does this president not understand that the Justice Department is not a tool of his own personal power?” Sen. Mark R. Warner (D-Va.) said on CNN in response to Trump’s statement calling on Sessions to investigate the op-ed author’s identity.

“That is one of the reasons why I think you’re seeing not only Republican members, but what appears to be a lot of folks in the White House, have real concerns about this president’s stability,” Warner added.

Pence has also been something of a “firefighter,” as one Republican from his home state termed it during the campaign, scrambling to put out the conflagrations caused by some of Trump’s more impolitic remarks.

In a speech to the national conference of the American Legion last month, Pence praised the late senator John McCain’s “lifetime of service,” days after Trump had prompted a torrent of criticism by issuing a belated proclamation honoring the Arizona Republican and Vietnam POW.

While Pence has drawn criticism for his approach to defending Trump, some see a political upside for the vice president.

“I think Pence has a smart strategy of sticking by the president’s side and doing as he’s told,” said Kate Andersen Brower, who examines the relationship between the two in her book “First in Line: Presidents, Vice Presidents, and the Pursuit of Power.” “He is an effective defender in part because he hasn’t been seen as someone who is caught up in the drama in the West Wing. There is very little leaking from his staff; they operate in a protective bubble.”

In one sign of how he has been seemingly insulated from some of the larger controversies engulfing the Trump administration, Pence said on “Face the Nation” that he has not been asked to sit down for an interview with special counsel Robert S. Mueller III amid the probe into Russian interference in the 2016 election — but that he would be “more than willing” to do so.