Karl Rove, the former White House senior adviser to former President George W. Bush, appeared on Fox News' special coverage of the South Carolina primary on Saturday and reacted to Democratic presidential candidate Joe Biden's projected win.

"Joe Biden had to win. If he didn't win tonight, he was out. He was gone," Rove told host Bret Baier. "The real question is going to be, what's the margin and what's the public reaction going to be to that margin?"

BIDEN FIGHTS FOR SURVIVAL IN SOUTH CAROLINA PRIMARY, SANDERS LOOKS TO EXTEND WINNING STREAK

Fox News projects that Biden will win Saturday's primary decisively, reflecting earlier polls indicating he had a significant lead over Sen. Bernie Sanders that is buoyed by his support among African-American voters.

Rove was hesitant to say South Carolina gives Biden momentum heading into Super Tuesday.

"But we've got to be careful about Tuesday, temper the impact of this on Tuesday," Rove said. "First of all, it is only three days and in California and Texas, in particular, a lot of the vote has already been cast. By the time early voting closed in Texas, probably 40 to 45 percent of the total Democratic primary vote had been cast."

The former White House official also noted former New York City Mayor Mike Bloomberg's impact on the race, saying he could siphon votes away from Biden.

Bloomberg's campaign will host more than 2,400 events across 30 states in a show of force before Super Tuesday, the first time the former mayor's name will appear on the ballot.

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"And then we have Mr. Bloomberg, who has a huge impact on Joe Biden on Tuesday, because the sense is [that] every vote Bloomberg gets comes out of Biden's hide, and we'll see who does better on Tuesday, Bloomberg or Biden," Rove said. "But I got to tell you, my gut tells me that the 800 million to a billion dollars that [...] Mike Bloomberg will spend by the end of the night on Tuesday night is probably going to bring him second [...] in a few places with more likely thirds in most places."

Fox News' Adam Shaw, Marisa Schultz and Paul Steinhauser contributed to this report.