Former White House chief strategist Steve Bannon believes a Democratic ticket of U.S. Sen. Kamala Harris of California and former U.S. Rep. Beto O’Rourke of Texas has the best shot to unseat President Trump in the 2020 presidential election.

Bannon made his claim Friday during an interview with CNBC. But he also said he believes Trump will likely be re-elected.

"I think the best they're going to have, and I don't think these people will defeat him, I think a combination ... of [Kamala] Harris for president and Beto O'Rourke for VP is a way to mobilize their base and give it the best shot," Bannon said on CNBC's "Squawk Box."

Neither candidate has suggested possible running mates.

The Democratic field for the 2020 presidential election is packed with at least a dozen candidates. Speculation is still mounting over whether former Vice President Joe Biden will launch a White House bid.

Bannon said that if no clear candidate has broken out of the pack that can take on Trump “one-on-one” by the fall of 2019, Democrats may have to bring back Hillary Clinton, Politico reported.

"People should not count her out," he said. "She's going to be sitting in the bullpen waiting for the call."

Trump has already launched an offensive against his potential rivals, Bannon said, taking verbal jabs at U.S. Sen. Elizabeth Warren, D-Mass.

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"She's probably got some of the most well-formed policy positions, particularly in comparison to some of the other candidates on the left," Bannon said. "He's basically blown her up already. She's in single digits, and I don't think she'll break out."

Trump has also bashed O’Rourke for his hand movements during his candidacy announcement.