Former Republican presidential candidate Mitt Romney meets with people at a rally for Ohio Gov. John Kasich on March 14 in Westerville, Ohio. Although Romney campaigned with Kasich in Ohio, he now says the only way to prevent Donald Trump from gaining the 2016 GOP nomination is to vote for Sen. Ted Cruz (R-Tex.), in hopes for an open convention. (Matt Rourke/AP)

While Gov. John Kasich (R-Ohio) headed to the second of three long-scheduled town halls in Utah, Mitt Romney announced that he'd be voting for Sen. Ted Cruz (R-Tex.) in this coming Tuesday's caucuses.

"The only path that remains to nominate a Republican rather than Mr. Trump is to have an open convention," Romney explained on his Facebook page. "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.  I like Governor John Kasich. I have campaigned with him. He has a solid record as governor. I would have voted for him in Ohio. But a vote for Governor Kasich in future contests makes it extremely likely that Trumpism would prevail."

The call for an open convention by the former Massachusetts governor and 2012 GOP nominee contradicted messages that Kasich and Cruz were pressing as they campaigned ahead in Tuesday's Western contests. Cruz would need to win around 78 percent of the delegates available in coming primaries to win the nomination outright. Nonetheless, he claims that a delegate win, not an open convention, is his goal.

"Only two campaigns have a plausible path to the nomination: ours and Donald Trump's," he told supporters at his Tuesday night election rally in Houston. "Nobody else has any mathematical possibility whatsoever."

Kasich, meanwhile, is pointing to the late-voting Midwestern and Northeastern states to argue that Cruz's best primaries are behind him. Cruz, who lost every Southern primary outside his native Texas, has outperformed Trump in caucuses and Western states, but underperformed him in places like Ohio, Vermont and Massachusetts. Kasich, who has rarely been attacked on the trail or in ads, enjoys the biggest crossover support from Democrats and highest favorable ratings of any remaining Republican candidate.

Yet Utah, where Kasich has several key endorsements, is seen as the sort of place where he can only hurt Cruz. The Beehive State holds binding "winner-take-most" caucuses, where any candidate who wins more than 50 percent of the vote grabs all 40 available delegates. If no candidate reaches a majority, the delegates are distributed proportionately.

There's been no public polling of Utah since the primaries were narrowed down to three candidates, but there is strong evidence, based on the vote so far by Mormon Republicans, that Cruz has an advantage. (Trump fared terribly in the more Mormon parts of Nevada, Idaho and Wyoming.) Were Cruz to take 40 Utah delegates, he'd cut back into the lead Trump built on March 15. Were he to win 49 percent, he'd take just 20 delegates.

After March 22, the primaries shift to Wisconsin, then to a quintet of Northeastern states.

Romney's own vote and advice cut against Kasich's theory of the primary, and Cruz's confidence -- though they do allow the Texan to claim that the party establishment is acknowledging him as the stop-Trump candidate.

In Utah, Kasich has so far offered the same pitch that sold well in Michigan and Ohio, but poorly in the South. When one voter asked why he canceled a debate that had been scheduled for Monday in Salt Lake City, Kasich insisted that voters would get more from direct campaigning than from a debate Trump had already canceled on.

"If we don't have the number one guy there, there's no point in having a debate," said Kasich. "I can use my time more effectively by doing things like this."