Republican Sen. Lindsey Graham warned incoming Sen. Mitt Romney Wednesday that publicly opposing President Trump would "hurt him and Utah." Graham, a critic-turned-ally of the president, responded to the opinion piece by Romney in The Washington Post saying that Mr. Trump "has not risen to the mantle of the office."

"If he's going to be the critic from Utah, it's going to hurt him and Utah," Graham said in an interview with Brian Kilmeade on Fox News Radio. Graham said that Mr. Trump is accessible and open to discussing policy. Graham has met with Mr. Trump to try to convince the president not to withdraw troops from Syria, although those attempts have so far been unsuccessful.

However, Graham said, Mr. Trump would not be willing to work with Romney "if he believes you are out to get him." Mr. Trump mocked Romney in a tweet on Wednesday morning, comparing him to former Sen. Jeff Flake, a frequent critic of the president.

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"Here we go with Mitt Romney, but so fast! Question will be, is he a Flake? I hope not. Would much prefer that Mitt focus on Border Security and so many other things where he can be helpful. I won big, and he didn't. He should be happy for all Republicans. Be a TEAM player & WIN!" Mr. Trump wrote.

Graham also said that those applauding Romney's opposition to Mr. Trump would turn on him as soon as he began casting conservative votes.

"What you got to learn from Kavanaugh, it's really not about Trump, it's about us. It's about conservatism," Graham said, referring to U.S. Supreme Court Justice Brett Kavanaugh, who was accused of sexual misconduct before his confirmation. Graham unloaded on Democrats during Kavanaugh's hearings, accusing them of cooking up allegations in response to the judge's conservatism.

Graham also urged Romney to "remember what they tried to do to you," possibly referring to criticism of Romney after he appeared to be in contention for the secretary of state post before Mr. Trump took office.

"Remember what they tried to do to you, Mitt. When they got through with you, you were a bad guy. The truth is you're a good guy, but in their world you will always be a bad guy if you cross them on policy," Graham said.