Mitt Romney is blasting out robo-calls on behalf of GOP presidential candidate Ted Cruz in the two Western states holding primary contests Tuesday – dismissing underdog candidate John Kasich in the process, all in the name of thwarting Donald Trump.

The 2012 Republican presidential nominee has recorded calls for the Texas senator in Arizona and Utah. In them, he declares, “At this point, a vote for John Kasich is a vote for Donald Trump."

The calls follow Romney on Friday throwing his support behind Cruz – at least for now -- and saying he represents the best chance at prolonging the election and forcing an open convention in July.

Cruz, who enjoys broad support from top Utah leaders, could have the upper hand in the state, which awards 40 delegates on Tuesday. Trump, though, has been rallying crowds in Arizona, which awards a prized winner-take-all batch of 58 delegates on Tuesday as well.

In Utah, Romney says he likes Kasich but plans to vote for Cruz on Tuesday, suggesting his candidacy is the only one right now that can hold Trump below the 1,237 threshold for clinching the nomination.

“At this stage, the only way we can reach an open convention is for Senator Cruz to be successful in as many of the remaining nominating elections as possible,” Romney said on Facebook on Friday.

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While Romney cuts robo-calls on behalf of Cruz, Utah Gov. Gary Herbert also endorsed Cruz on Monday, giving the Texas senator support from another key political figure in the state ahead of the presidential caucuses Tuesday.

“Ted Cruz is a consistent conservative who understands the importance of federalism. I’m confident he will work to limit the federal government when it comes to education, public lands and other issues where states can do better than the federal government,” he said on Facebook.

Kasich’s campaign, meanwhile, has knocked Romney for his decision to throw his weight behind Cruz.  

"The fact is the establishment has gotten it wrong this entire primary and it is unfortunate to see that Mitt Romney is getting bad political advice. John Kasich is best positioned to stop Donald Trump in the Midwest, Mid-Atlantic and Pacific coast states,” Kasich chief strategist John Weaver said Friday in a statement.

Trump continued to rail against Romney for his election intervention, tweeting: “Mitt Romney is a mixed up man who doesn't have a clue. No wonder he lost!”

Fox News’ Daniel Gallo and The Associated Press contributed to this report.