The long, sometimes-contentious relationship between Donald Trump and Chris Wallace will be on full display Tuesday night as the Fox News anchor moderates the president’s first debate with Democratic challenger Joe Biden.

Over the course of his presidency, Trump has lavished praise on Fox’s biggest opinion stars, shouting out Sean Hannity, Laura Ingraham and Jeanine Pirro at his campaign rallies. In contrast, the president has attacked Wallace, a key member of the network’s news division, in extremely personal terms.

“It’ll be unfair, I have no doubt about it,” Trump told Fox News host Brian Kilmeade on Thursday morning, previewing the debate. “He’ll be controlled by the radical left. That’s what — they control him.”

It’s a claim that is roundly scoffed at by colleagues of Wallace, who worked long stints at NBC and ABC before Fox. “Chris Wallace has, for his entire career, been an independent journalist,” emphasized Carl Cameron, the network’s chief political correspondent until his retirement in 2017.

A month and a half before the Commission on Presidential Debates tapped Wallace to moderate the first of three presidential debates, he went toe-to-toe with Trump in a White House interview that many scored as a knockout victory for the journalist and something of an embarrassment for the president, who struggled to explain his response to the coronavirus pandemic as Wallace fact-checked him in real time.

“That’s not true, sir,” Wallace calmly maintained as Trump falsely claimed that the United States has the lowest coronavirus mortality rate in the world. The president attempted to dismiss as “fake news” Wallace’s statistic about the United States having the seventh highest rate in the world. “I don’t think I’m fake news,” Wallace said. “Well, there you are,” Trump retorted.

In an interview that aired July 19, "Fox News Sunday" host Chris Wallace asked President Trump about the coronavirus, upcoming elections and civil unrest. (The Washington Post)

Because of this clash and previous ones, Wallace is viewed skeptically by many of the president’s backers, who will be watching closely on Tuesday night when Wallace attempts to keep both Trump and Biden in line and on topic, in a format that will not allow for that kind of fact-checking.

"When we choose moderators, we make very clear to them that there’s a vast difference between being a moderator in a debate and being a reporter who is interviewing someone,” the debate commission’s co-chairman, Frank J. Fahrenkopf Jr. told CNN on Sunday. “When you’re interviewing someone, if they say something that is in direct opposition to something they said a week ago, your duty is to follow up and say, ‘Wait a minute, you didn’t say that a week ago.’ But that’s not the case for a debate.”

For their part, some Democrats have also expressed suspicion of Wallace, who seemed to show his Fox News leanings last week when he unveiled the five topics that will be discussed at the debate. One of them, described as “Race and Violence in Our Cities,” seemed to echo a story line of Democratic-led cities spiraling into lawlessness amid this year’s racial-justice protests that is popular with the network’s weeknight opinion hosts.

That’s why the Biden campaign is anticipating the Wallace-moderated debate to have a “Fox News framing” and preparing the candidate for that dynamic, a Democratic strategist with knowledge of the campaign’s plans told The Washington Post.

Wallace said on his “Fox News Sunday” broadcast this week that his goal for Tuesday’s debate is to be “as invisible as possible.”

“I’m trying to get them to engage, to focus on the key issues, to give people at home a sense of, ‘why I want to vote for one versus the other,' ” he said. "But if I’ve done my job right, at the end of the night, people will say, ‘That was a great debate. Who was the moderator?’ ”

If the president lies on Tuesday night, “I think Chris Wallace will be required to mediate some of that,” Cameron said. “If he were to let nonsense go, the credibility of the debate and the credibility of Chris Wallace will take a hit.”

“Clearly, people are going to criticize him for whatever he does, but I’ll bet you that he does an extremely good job and that most people say they’re so glad that Chris is doing that first one,” said Tom Bettag, a University of Maryland journalism school teacher who served as executive producer when Wallace guest-hosted ABC’s “Nightline” and worked with his father, “60 Minutes” legend Mike Wallace, at CBS News.

Bettag said that Wallace sees himself as a reporter, first and foremost, and “does his homework more diligently than almost anybody else that I’ve ever seen.”

The president has repeatedly compared Wallace, unfavorably, to his larger-than-life dad, saying that the younger Wallace “will never be his father."

But Wallace has never really engaged with the president’s attacks, making it a fairly one-sided beef. “My reaction is always, ‘one of us has a daddy problem, and it’s not me,' ” Wallace joked to an audience at the Advertising Week conference last September.

Wallace has also indicated that he sees Trump as a performer or television programmer, suggesting that he takes him less than seriously as a politician. “It’s the Trump show,” he told an audience last year. “You can love him or hate him, but it is . . . the greatest, most compelling, riveting reality show that we’ve ever seen.”

Wallace joined Fox News in 2003, after 14 years at ABC News and a long run at NBC News before that. “He went to Fox, and he didn’t change who he was,” Bettag said.

Wallace’s research-based, tough-but-respectful approach to debate moderation was on display in August 2015, when he, anchor Bret Baier, and then-host Megyn Kelly moderated the first debate of the 2016 Republican presidential primary. Wallace grilled Trump about his past corporate bankruptcies: “With that record, why should we trust you to run the nation’s business?” he asked. Mocking Wallace’s comments about lenders getting ripped off, Trump told him, “You’re living in a world of the make-believe, Chris.”

The clearest precedent for Tuesday night’s matchup is the Oct. 19, 2016, general election debate between Trump and Hillary Clinton, also moderated by Wallace.

“It was an enormously stressful thing,” Wallace told an audience at the Columbia University School of Journalism in February. “More than anything I’d ever done, there were moments when I thought, I don’t know if I can handle this.”

Fox News anchor Chris Wallace repeatedly asked the candidates and the audience to behave at the third and final presidential debate on Oct. 19, 2016. (Gillian Brockell/The Washington Post)

Michael D. McCurry, the former White House press secretary who served as co-chair of the debate commission in 2016, said that Wallace was selected for the role after “Fox made a legitimate argument that one of their anchors had never been selected as a debate moderator.” Baier was also considered, he said.

“I think Wallace got pretty good marks for his role as a moderator in 2016. I think he will again this time around,” McCurry said.

But, he added: “It ain’t about the moderator. It’s about the candidates. So, it will be up to Trump and Biden to make this a useful conversation for Americans.”

Cameron sees his former colleague’s role a little differently. “I hope to God that Chris really kicks his a--,” he said.