(CNN)Mitt Romney recorded robocalls for both Sen. Marco Rubio and Gov. John Kasich's presidential campaigns in states that are voting on Tuesday, CNN has confirmed.
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Romney cuts get-out-the-vote robocalls for Rubio and Kasich
It's part of an escalating effort by Romney to block Donald Trump from securing the Republican presidential nomination.
The calls recorded on behalf of Rubio, which were first reported by The New York Times on Monday night, are going out in all four states voting Tuesday. On Tuesday, Kasich's campaign spokesman Chris Schrimpf told CNN the former Massachusetts governor also recorded calls in Michigan on behalf of the Ohio governor.
Romney's message may prove more effective in the crop of states voting Tuesday -- most notably Michigan and Idaho -- than it might be to the broader GOP electorate.
Romney's dad, George Romney, was the former Michigan governor, and many voters in the Mitten State still hold on to some affection for the Romney family.
Meanwhile, Idaho has a sizable Mormon population, which helped Romney -- who is Mormon -- trounce rival Rick Santorum there in 2012.
The robocalls follow Romney's withering denunciation of Trump in a speech at the Hinckley Institute Thursday, where he called Trump a "phony" and a "fraud," and vowed to work to prevent Trump from becoming the Republican standard bearer.
The calls do not represent an outright endorsement for either candidate, and a spokesperson for Romney said the 2012 GOP nominee would be willing to help Sen. Ted Cruz as well.
"Gov. Romney has offered and is glad to help Sen. Marco Rubio, Sen. Ted Cruz, and Gov. John Kasich in any way he can," the spokesperson told CNN. "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."
The spokesperson also confirmed the substance of the message, in which Romney tells voters to back "a candidate who can defeat Hillary Clinton and who can make us proud."
"If we Republicans choose Donald Trump as our nominee, I believe that the prospects for a safe and prosperous future would be greatly diminished," Romney says in the calls, which use a near identical script for Kasich and Rubio. "And I'm convinced Donald Trump would lose to Hillary Clinton."