An adviser for Ohio Gov. John Kasich reportedly cautioned President Trump Thursday after the president said he'd welcome a 2020 challenge from his former political adversary.

“Be careful what you wish for,” John Weaver, a chief political strategist, told CNBC after the president said he’d welcome a run by either Kasich or outgoing GOP Arizona Sen. Jeff Flake.

Trump's comments came during an exclusive interview with Fox News’ Harris Faulkner on Thursday.

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“So you mentioned Ohio, so I'm going to bring up John Kasich and I'm going to bring up Arizona Senator Jeff Flake. Because they say they may run against you in 2020,” Faulkner said.

“I hope so,” Trump replied.

Kasich is “open-minded” about potentially campaigning as an Independent versus within the GOP, Weaver also told CNBC, before noting that Kasich “is a Republican.”

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Representatives for Kasich did not immediately return Fox News’ request for comment.

The Ohio governor has recently discussed a possible White House run, telling ABC’s “This Week with George Stephanopoulos" earlier this month that “we’re seriously thinking about it.”

“We're seriously talking about it with family and friends and political allies who have come to me about this,” Kasich said.

Fox News’ Alex Pappas contributed to this report.