By Steve Holland
DETROIT (Reuters) - Chief rivals to U.S. Republican presidential front-runner Donald Trump assailed him for shifting positions on the issues at a debate, but said in the end they would reluctantly support him if he were their party's nominee.
Under questioning by Fox News Channel moderators on Thursday, U.S. Senators Marco Rubio of Florida and Ted Cruz of Texas and Ohio Governor John Kasich made the promise despite efforts by party elders to build an anti-Trump coalition of Republican voters to pick someone other than the incendiary New York billionaire.
Hours earlier 2012 Republican nominee Mitt Romney in a speech blasted Trump, a former reality TV show host, as an unelectable fraud whose nomination would ensure victory for Democratic front-runner Hillary Clinton in the Nov. 8 election to succeed Democratic President Barack Obama.
Tempers escalated quickly at the two-hour debate and, as in previous encounters, the battle descended into schoolyard taunts between Trump, Rubio and Cruz with accusations of lying and even a reference to male genitalia.
While Trump's three rivals followed party dogma, insisting they would set aside their concerns and rally around the ultimate nominee, they said they did so reluctantly if Trump were to emerge as the candidate for the general election.
"Sometimes he makes it a little bit hard," said Kasich, 63.
Trump, asked if he would support the Republican nominee if it was someone other than him, seemed startled by the question given the momentum behind him, but eventually said, "Yes I will." Trump, 69, defended himself from Romney's blistering rebuke and called Romney a failed candidate.
With the Florida and Ohio primary votes looming on March 15 as make-or-break for the anti-Trump forces, Trump provided some ammunition to his critics.
Trump shrugged when presented with videotaped evidence from the moderators that he had shifted positions on the Iraq war, immigration and whether to admit refugees from the Syrian civil war.
"You have to show a degree of flexibility," he said.
Both Rubio and Cruz pounced.
"I hope we don’t see yoga on this stage," Cruz said. Replied Rubio: "Well, he's very flexible so you never know."
It remained to be seen whether the debate would prove to be damaging to Trump. The runaway front-runner to date has been immune from criticism that other politicians normally face, for instance, over flip-flopping on issues.
While Trump saw the greatest number of overall mentions on social media site Twitter, an analysis showed that 63 percent of the tweets expressing an opinion on him were negative, according to social media analytics firm Brandwatch which separated objective tweets from opinionated tweets in its analysis.
The rating marks a decline in positive sentiment for Trump. In the last two Republican debates, Trump broke even in terms of positive and negative mentions, according to the firm's analysis, while he enjoyed a 62.5 percent positive sentiment rating during the Republican debate before that.
IMMIGRATION, FOREIGN WORKERS
Rubio, 44, and Cruz, 45, questioned Trump's immigration policy and his use of foreign workers at his exclusive Mar-a-Lago resort in Palm Beach, Florida.
Cruz demanded Trump release an audiotape of an off-the-record session he had with New York Times editorial writers on Jan. 5.
Cruz and others have suggested that in the session Trump might have been more flexible on immigration than in public statements insisting he would build a wall between the United States and Mexico and deport 11 million illegal immigrants.
Trump refused to release the tape but said he would be flexible, for instance, on the height of the wall. He also abruptly changed his position on foreign workers, saying more of them who are highly skilled should be allowed to remain in the United States.
Rubio pressed Trump on the foreign workers he has imported to work at his Palm Beach resort, jobs he said could go to Americans. Trump said the workers were for a short November-to-March season.
"People don’t want a short-term job," Trump said. "So we bring people in and we send people out."
'GIVE ME A BREAK'
Rubio asked Trump why he does not bring his clothing-making operations to the United States from China and Mexico if he is so interested in bringing jobs home, a central tenet of his unconventional campaign.
"This little guy has lied so much about my record," Trump said in response to Rubio, adding that he had begun bringing some clothing operations home from overseas.
But Rubio persisted: "The answer is he’s not going to do it ... The reason he makes it in China and Mexico is because he can make more money on it."
Fox News moderator Megyn Kelly, who famously clashed with Trump at the first Republican debate last August, generated a fresh exchange in pressing Trump to explain his involvement with Trump University, a now-defunct online education company that has faced lawsuits from people who feel they paid out money for Trump U and got nothing in return.
"Give me a break," said Trump. "Let's see what happens in court."
Rubio accused Trump of fleecing everyday Americans for personal gain.
"He's trying to do to the American voter what he did to the people who signed up for this course," Rubio said.
The debate went down a negative path early on when Trump responded to Rubio's contention last month that Trump had "small hands."
"Look at these hands," Trump said, flashing his two hands to the crowd. He dismissed any suggestion he might be small elsewhere, Trump said: "I guarantee you there is no problem."
(Reporting by Steve Holland; Additional reporting by Ginger Gibson, Emily Stephenson and Amy Tennery; Editing by Howard Goller)