Romney’s warning is coming to a phone near you in four states voting Tuesday: Michigan, Idaho, Hawaii and Mississippi.
In the call, which was first reported by the New York Times, Romney notifies listeners that he is calling for Rubio and asks them to choose “a candidate who can defeat Hillary Clinton and who can make us proud.”
“If we Republicans were to choose Donald Trump as our nominee, I believe that the prospects for a safe and prosperous future would be greatly diminished — and I’m convinced Donald Trump would lose to Hillary Clinton,” Romney says.
A source close to Romney told NBC News Monday that the former Massachusetts governor “has offered and is glad to help Senator Marco Rubio, Senator Ted Cruz, and Governor John Kasich in any way he can. He’s been clear that he believes that Donald Trump is not the best person to represent the Republican Party and will do what he can to support a strong nominee who holds conservative values to win back the White House.”
Romney, who has not endorsed a candidate, began his anti-Trump crusade last week, announcing during a speech in Utah that the GOP front-runner is a phony, fraud and a misogynist.
To which Trump, recalling Romney’s solicitation of his endorsement in 2012, responded: “I could have said, ‘Mitt drop to your knees,’ and he would have dropped to his knees.”
This story originally appeared on NBCNews.com.