Dana Perino can punch and parry with the best of them. But she could be better at ducking.

In 2008, when Ms. Perino was the White House press secretary for President George W. Bush, she got clocked in the face with a boom microphone in the scuffle that broke out after a journalist threw his shoes at Mr. Bush.

“I had a black eye for six weeks,” Ms. Perino, now an anchor for Fox News, said in an interview last week from her sun-dappled Upper West Side apartment.

That kind of fracas — and the nearly two years she spent taking questions from reporters in the White House briefing room — may be good preparation for her next act: moderating the Republican presidential debate on Wednesday in Simi Valley, Calif.

It will be the biggest moment for Ms. Perino at Fox News since she began co-hosting “The Five” in 2011. Not known for being as provocative or partisan as many of her colleagues behind the desk, Ms. Perino, 51, has spent a good part of the last decade trying to thrive as a Bush Republican working for a network where loyalty to former President Donald J. Trump is often the ticket to high ratings and the career advancement that accompanies them.

Ms. Perino, who also co-hosts the two-hour morning news show “America’s Newsroom,” is one of the relatively few White House aides to make the leap from politics to news anchor. She says she modeled her transition after two other former West Wing staff members who had made the transition — George Stephanopoulos, the ABC News anchor who served as Bill Clinton’s communications director, and Diane Sawyer, also of ABC, who was an assistant to Richard M. Nixon.

Current and former colleagues said that she has managed to persevere at Fox by being neither a Trump supplicant nor fierce critic. During the raucous discussions on “The Five,” she can often be seen ducking the fray, flashing a knowing smile as her co-hosts mock Mr. Trump’s liberal antagonists.

And she feels no need to deliver the pro-Trump monologues that other conservative hosts have made a staple of their programs.

“If she tried to fake it, she knows people would see through her,” said Tony Fratto, a former Bush administration official who worked with Ms. Perino in the White House and remains a friend. Mr. Fratto said that Ms. Perino’s independence was something she was determined to keep while working her way up at the network.

“She’s very rational and respectful of people with different views,” he said.

Ms. Perino is one of the few Fox anchors to have never interviewed Mr. Trump. And she doesn’t appear especially eager to do so.

When Dominion Voting Systems sued Fox News over its promotion of conspiracy theories relating to Mr. Trump’s loss in 2020, some of Ms. Perino texts with her colleagues became public, revealing how little she thought of the former president and his claims that extensive voter fraud cost him the election. She said as much on air as well and told Mr. Fratto, who was representing Dominion at the time, in one text exchange how she was being threatened. “The maga people are crushing me for it,” she wrote, “and I even have death threats now.”

Asked last week whether she would prefer it if Mr. Trump participated in this week’s debate — he will skip it, as he did the debate last month in Milwaukee — Ms. Perino wasn’t exactly brimming with enthusiasm.

“Sure,” she said. If she were advising Mr. Trump, she said, she would encourage him to go. But she also said she believed his absence presents his rivals with opportunities to break out in ways that have eluded them so far.

She said she believed that the last debate, which was hosted by her Fox News colleagues Bret Baier and Martha MacCallum, was not particularly successful for the candidates because they spent so much time interrupting each other.

“The candidates made a decision to break the rules, and to talk over each other,” she said.

She will not shy away from interrupting them if they do the same, she said. And she does not fear playing the role of schoolmarm if she needs to. (Her co-moderator in the debate, Stuart Varney of Fox Business, is no shrinking violet either.)

“I’m happy to be that,” she said, adding that she hopes that isn’t necessary. “I think that for them, they should not want that either, right, because it didn’t help them. If you think about that debate, there was no consensus of who won.”

Preparing for the debate can be a thankless task, as many moderators before her have discovered. The candidates often dismiss the carefully drafted questions the moderators have written.

Friends and former colleagues said that Ms. Perino has a knack for preparedness that exceeds most.

“When she would prepare President Bush for press conferences, you’d go through the anticipated questions,” said Ed Gillespie, who served as counselor to the president during Mr. Bush’s second term. “A question would come, and it would be one that Dana said would come. And then there would be another that Dana said would come. And a third. And every single question would be one that Dana said would come.”

Her Fox colleague Greg Gutfeld, a fellow host on “The Five,” said he pokes fun at her for how she comes to the show armed with a notebook full of ideas based on the news articles that are driving the day. “Unlike me, she reads the articles. She’s like the grade-A student in your class,” Mr. Gutfeld said. “She doesn’t throw it in your face. But she’s prepared.”

Former colleagues said that Ms. Perino wasn’t one to pull her punches when it came to briefing the president, which she always came to extensively prepped.

“If you’re preparing the president, you have to do it nicely, of course, since he’s the one who was elected,” said Condoleezza Rice, the secretary of state during Mr. Bush’s second term. “But you also have to be willing to say, ‘Mr. President, that answer isn’t going to fly.’ Dana did that. And I think President Bush respected her for it.”

Ms. Perino’s second act as a news anchor puts her back where she started her career right out of college. After working as a disc jockey on the overnight shift at a country music station in Pueblo, Colo., she graduated from the University of Southern Colorado and moved to the Midwest, eventually landing a job as a reporter for a television station in Champaign, Ill. She decided a life of covering local news — holiday parades, municipal government meetings — wasn’t for her.

“I didn’t see how you could get ahead quickly. And I had an ambition,” she explained, adding that she never saw herself becoming “the replacement for Tom Brokaw.” When she left local news, she said, she thought that would be the end of her time in television news. “I really thought if I do this I’ll never work in TV again.”

Her first big job in the Bush White House came in 2006 when, after holding a series of communications jobs throughout Washington, she was hired at age 34 as the deputy press secretary under Tony Snow, a former host of “Fox News Sunday.” He stepped down in 2007, after being diagnosed with colon cancer. Mr. Bush named Ms. Perino as the new press secretary.

“She can handle you all,” the former president told the room of journalists. Now, she is the journalist. And the G.O.P. presidential candidates will have to handle her.