Washington (CNN) On Sunday, Sen. Jeff Flake, R-Arizona, was asked whether he thinks someone should challenge President Donald Trump in the 2020 Republican primary.

"Yes, I do. I do," Flake told "Meet the Press" host Chuck Todd . "I mean, it would be a tough go in a Republican primary. The Republican Party is the Trump party right now. But that's not to say it will stay that way."

Who could that someone be? Obviously, Flake, who was all-but-forced into retirement after his attacks on Trump led to an open revolt against him by the base of the party, wants it to be him. (He has been very coy about his own future political plans.)

And he's certainly on the list of potential Trump primary challengers. Here's my ranking of the top three -- in order of most likely to least likely to actually run.

1. John Kasich

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