Mitt Romney, John Kasich

FILE - In this April 27, 2012 file photo, Republican then-presidential candidate Mitt Romney, right, and Ohio Gov. John Kasich participate in a roundtable discussion in Westerville, Ohio.

(Jae C. Hong, The Associated Press)

CLEVELAND, Ohio -- Marco Rubio isn't the only Republican presidential hopeful getting an assist from Mitt Romney in Tuesday's Michigan primary.

Romney, who has become a vocal leader in the GOP establishment's effort to stop front-runner Donald Trump, also taped robocalls for Ohio Gov. John Kasich.

"Hello, this is Mitt Romney calling, and I'm calling on behalf Kasich for America," the former Massachusetts governor and 2012 Republican presidential nominee, says at the beginning of the call, audio of which was shared by the Kasich campaign.

"Today you have the opportunity in Michigan to vote for a Republican nominee for president," Romney continues. "These are critical times that demand a serious, thoughtful commander-in-chief. If we Republicans were to choose Donald Trump as our nominee, the prospects for a safe and prosperous future would be greatly diminished -- and I'm convinced Donald Trump would lose to Hillary Clinton. Please vote today for a candidate who can defeat Hillary Clinton and who can make us proud."

Kasich spokesman Rob Nichols said the calls launched Tuesday morning.

The script is similar to one Romney used in calls paid for by the Rubio campaign. The Florida senator, like Kasich, is an establishment-friendly candidate hanging on by tooth-in-nail in the GOP presidential race. The Washington Post and others reported Monday evening that Romney was going to bat for Rubio but stopping short of an endorsement and offering to help Kasich and Texas Sen. Ted Cruz, too.

Romney last week delivered a speech calling on voters in future primary and caucus states to support Cruz, Kasich or Rubio in an effort to deny Trump the nomination.

Elite Republicans worry that Trump's rhetoric and shifting positions will cost the party in a general election against Clinton, the Democratic front-runner.

Kasich hopes a strong finish Tuesday in Michigan will set him up for a win over Trump next week in Ohio, his home state, where polls show a close race.