By Andy Sullivan and Alana Wise
WASHINGTON (Reuters) - Republican Mitt Romney said on Friday he would vote for U.S. Senator Ted Cruz in Utah's presidential nominating contest, but the party's 2012 election standard-bearer stopped short of an official endorsement as he urged voters to deny the nomination to front-runner Donald Trump.
In a Facebook post, Romney said a vote for Cruz in Utah's caucus on Tuesday was the best way to prevent Trump from locking down the nomination, which would give opponents a chance to select another candidate at the party's July convention.
"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 wrote.
Romney did not offer any praise for Cruz, who emerged as a favorite of the party's most ardent conservatives after clashing with party leaders in Washington. Romney did not say whether or not he would campaign with Cruz, a first-term senator from Texas.
Trump responded quickly. "Mitt Romney is a mixed up man who doesn't have a clue. No wonder he lost!" he wrote on Twitter.
Cruz, acknowledging the tepid nature of Romney's support, said the pledged vote enforces the idea that his campaign is the only one that can beat Trump, likening a vote for Ohio Governor John Kasich, the third remaining Republican contender, to tacit support for Trump.
"In my book, when someone says ‘I’m voting for you, and I encourage everyone else to vote for you,’ that’s pretty darn good," Cruz, a self-styled Washington outsider, told reporters in Arizona. "And I’ll take that and take that happily." Arizona also holds its nominating contest on Tuesday.
"As Mitt Romney observed today, if you want to beat Donald Trump, Cruz is the only campaign that can do it. That’s why he’s voting for me in Utah," Cruz said.
Romney has emerged as one of the most prominent critics of Trump, the billionaire businessman and reality-TV star who has become the surprise front-runner in the battle to secure the Republican nomination for the Nov. 8 election. Romney, who lost to Democratic President Barack Obama in 2012, called Trump a "fraud" and a dangerous demagogue who would lose to Hillary Clinton, the Democratic Party front-runner, in November.
"Today, there is a contest between Trumpism and Republicanism," Romney wrote, adding that Trump has encouraged racism, misogyny and violence. "I am repulsed by each and every one of these," he wrote.
Kasich's campaign called Romney's turn to Cruz the result of "bad political advice." "This is just the old establishment trying again to game the political system, but John Kasich's defeated the Republican establishment his entire career," the campaign said.
Romney's support for Cruz comes a day after U.S. Senator Lindsey Graham threw his support behind the Texas senator, saying in similar fashion that Cruz has the best chance of stopping Trump, even though he thinks Kasich would have a better chance of winning in November's general election.
Trump has continued to notch victories in the state-by-state nominating process as Republicans have failed to unite behind Cruz or Kasich. At this point, those who oppose Trump say their best bet is to prevent him from securing the 1,237 delegates he needs to lock up the nomination before the convention in Cleveland. So far, Trump has won 678 delegates.
Cruz would need to win 81 percent of the remaining delegates to reach a majority, according to the Cook Political Report. It is impossible for Kasich to reach 1,237 delegates, according to the nonpartisan election tracker.
Romney said Kasich has a "solid record" as a governor and he would have voted for him in Ohio last Tuesday.
(Additional reporting by Richard Cowan; Editing by Grant McCool and Leslie Adler)