It's the big question regarding cable news host Bill O'Reilly: If he's dismissed from Fox News — as several reports indicate he may be — who will replace him?

Asking such a question was unthinkable before a New York Times story just three weeks ago revealed Fox or O'Reilly had paid out $13 million to settle five harassment cases against him.

The Rupert Murdoch-owned Wall Street Journal reported on Tuesday night that Fox News is preparing to part ways with O'Reilly in the coming days. Earlier in the day, New York magazine and CNN reported the same.

O'Reilly denies any wrongdoing, saying the payments were made "to put to rest any controversies to spare my children.”

Fox faced a similar situation in January with the departure of Megyn Kelly to NBC despite a reported $100 million offer to her to stay. But Tucker Carlson has filled the void at 9:00 p.m. seamlessly, even generating higher ratings than Kelly, who finished 2016 as the second most-watched host in cable news behind O'Reilly.

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Replacing O'Reilly may be far trickier, given how long "The O'Reilly Factor" has been a staple on Fox News. The program began as "The O'Reilly Report" in October of 1996 before becoming "The O'Reilly Factor" months later. Kelly's former show, in contrast, had only been on in prime-time since 2013.

Four names are seen as the most likely candidates to fill O'Reilly's shoes if reports of his demise are true: "The Five" co-host and "Cashin' In" host Eric Bolling, "The Five" co-host and former White House press secretary Dana Perino, "The Five" co-host and former "Red Eye" host Greg Gutfeld and "Watters World" host Jesse Watters, a longtime producer and man-on-the-street interviewer on "The O'Reilly Factor."

All four have guest hosted for O'Reilly this year.

Bolling, a former commodities trader and staunch supporter of President Trump, has served in that capacity the most over the past few years.

Watters and Gutfeld, whose brands are more casual, comical and self-deprecating than O'Reilly or Bolling, have also been given plenty of at-bats.

Perino got her first opportunity on O'Reilly's first day on vacation last Wednesday. After handing over the reigns to Bolling on Thursday and Gutfeld on Friday, she was tapped to host the first two days of this week.

Ratings fell 23 percent with Perino, Bolling and Gutfeld hosting over the first four nights without the vacationing O'Reilly. Despite the dropoff, Fox still easily beat its cable news competition at 8:00 p.m. in total viewers and the prized 25- to 54-year-old demographic.

Perino has performed best from a ratings perspective with 3.15 million viewers on Monday, down 16 percent from O'Reilly hosting a week earlier.

Bolling saw a 16 percent drop from O'Reilly hosting the Thursday prior, registering 3.11 million viewers.

Gutfeld's Friday program was down 39 percent from the previous Friday when O'Reilly hosted, with 2.32 million viewers.

Another post-O'Reilly scenario, however, is a possibility: Replacing "The Factor" at 8:00 p.m. with "Tucker Carlson Tonight," a proven commodity in the 9:00 p.m. slot.

The move would be familiar for Carlson, who was the co-host of "Fox & Friends Weekend" as recently as last summer before taking over for the departed Greta Van Susteren at 7:00 p.m. in September.

Carlson performed so well both critically and in terms of ratings that he was chosen to replace Kelly at 9:00 p.m. in January, increasing ratings considerably in the time slot in the process.

Replacing Carlson at 9:00 p.m. would be the steady Sean Hannity, currently at 10:00 p.m., who has been with the network as a prime-time host since its inception in 1996. Hannity was Fox's 9:00 p.m. host until Kelly was moved into that position in 2013.

As for 10:00 p.m., the network and any host being tapped for it would be relatively relieved of any pressure to perform up to O'Reilly's standards from a ratings or content perspective. Under this scenario, Fox could experiment on its own terms via rotating hosts for the foreseeable future until a permanent personality is decided upon.

If a program at 10:00 p.m. opens up, the competition may extend well beyond Bolling, Perino, Gutfeld and Watters.

Another "Five" co-host, Kimberly Guilfoyle, would undoubtedly be considered. Former CNBC star Trish Regan of the Fox Business Network would also likely be in the running, as would another former guest host for O'Reilly, syndicated radio host Laura Ingraham.

And then there's the possibility of moving another hit opinion show, "The Five," to 10:00 p.m., which would allow Perino, Bolling, Guilfoyle and Gutfeld to get a permanent hosting job in prime time, along with former Democratic strategist Bob Beckel.

In any scenario, replacing O'Reilly would be the most daunting task Fox News has ever faced.

The 67-year-old is the highest-rated cable news host of the past 15 years. Many would argue he's not just the 8:00 p.m. host, but an ambassador of the network via seemingly regular appearances on the broadcast networks, multiple best-selling books and nationwide tours with Dennis Miller and Watters doing sold-out comedy shows.

The good news for Fox is that its audience has a proven loyalty.

That loyalty to O'Reilly is exemplified in a Morning Consult poll released Wednesday.

Among those respondents who said they watch his show, 23 percent said it should be canceled while 58 percent think the should keep O'Reilly as host.

And with Trump bringing record viewers to cable news across the board, it may not matter quite as much who is sitting in the host chair with charged interest in political programming, at least for the time being.