Former Mississippi Gov. Haley Barbour said in a Fox News interview he believes it’s likely President Trump will be challenged in the 2020 Republican presidential primaries.

“I think it would be a mistake to assume there won’t be a Republican primary,” Barbour said Tuesday on “The Daily Briefing with Dana Perino.”

Trump, who remains popular in the Republican Party, has announced plans to run for re-election. But Barbour has questions..

“First of all, there is not a 100 percent chance that President Trump will run,” Barbour said. “There’s an assumption he will run. I wouldn’t bet against it. But I think it would not be smart to say there won’t be a primary whether Trump runs or not”

Other anti-Trump Republicans have called for Trump to be challenged, including Ohio Gov. John Kasich, who said Sunday he is seriously considering running.

"We're seriously thinking about it," Kasich said on ABC's “This Week with George Stephanopoulos." “We're seriously talking about it with family and friends and political allies who have come to me about this."

Kasich unsuccessfully sought the Republican nomination in 2016.

JEFF FLAKE ON 2020: 'SOMEBODY NEEDS TO RUN ON THE REPUBLICAN SIDE'

Another Republican mentioned as a potential anti-Trump challenger is outgoing Arizona Sen. Jeff Flake, who recently said that “somebody needs to run on the Republican side.” He referenced both Kasich and Nebraska Sen. Ben Sasse as other possible challengers.