Republican attacks escalate as Trump insists 'there is no problem' with his penis size

Donald Trump unleashed fiery, off-color rhetoric at the Republican debate after enduring a day of intense criticism by party leaders, as conservatives agonize over embracing his divisive candidacy or derailing his march to the nomination.

But despite escalated attacks against Trump by his rivals on the debate state, each one of them -- Senator Ted Cruz, Senator Marco Rubio, and Ohio Governor John Kasich -- acknowledged they would support the party's eventual nominee.

With the real estate tycoon apparently on a glide path to becoming the Republican standard-bearer, some panic has set in at the prospect of Trump winning the nomination.

Other operatives and voters said it is time, for better or worse, to rally around the man leading the pack.

With the bitter rivals gathered at a pivotal moment in the campaign, the debate attacks turned deeply personal, even vulgar. Trump made a startling if veiled reference to his genitals as he hit back against Rubio for mocking the size of Trump's hands.

"Nobody has ever hit my hands," Trump said as the raucous crowd laughed and booed.

"He referred to my hands. If they're small, something else must be small. I guarantee you there is no problem."

Rubio excused his own attacks by insisting it was Trump who opened the flood gates.

"Donald Trump has basically mocked everybody with personal attacks," Rubio said.

Trump's remarks, likely unprecedented in a US presidential debate, appeared as the nadir of a campaign season already notable for its unruly, coarse tone.

With Trump thrown on the defensive, he lashed out multiple times, at one point hurling insults and talking over his rivals.

"You've defrauded the people of Florida, little Marco," he said.

Florida votes on March 15 and is Rubio's firewall, even though Trump leads there in polls. If he can not win his home state, Rubio will find no path to the nomination.

Kasich, who is scrambling to avoid irrelevance in the fierce nomination contest, said he hoped the race could focus on important policy issues and not the "scrums" and personal debasement on display Thursday.

"People say wherever I go: 'You seem to be the adult on the stage,'" Kasich said.

With time running out to stop Trump, Mitt Romney -- who ran unsuccessfully against Barack Obama in 2012 -- on Thursday offered up some of the harshest criticism yet, lambasting Trump as unfit to be president.

Romney said a Trump nomination would enable a Democratic victory for the party's presumptive nominee Hillary Clinton.

"Donald Trump is a phony, a fraud," Romney said in a speech in Utah, as he urged voters to support one of the remaining candidates.

Trump, Romney said, "is playing the American public for suckers."

Trump wasted little time in striking back, calling Romney a "choke artist" and assailing him for "begging" for an endorsement, only to lose to Obama four years ago.

Romney still holds sway with certain elements of the party, but even Kasich downplayed the influence that the 2012 nominee would have on 2016.

"Mitt Romney is a great guy, but he doesn't determine my strategy," Kasich said at the debate.

- Trump 'disaster' -

The debate, broadcast on Fox News, took place in the largest city in Michigan, the biggest prize of the four states holding Republican primaries next Tuesday.

Whether or not Trump should carry the torch is now the crux of the GOP race, which he has dominated essentially since he jumped in eight months ago.

Cruz insisted "the stakes are too high" to let Trump be the nominee, arguing that Clinton will eat him alive ahead of the November election.

"Is this the debate you want playing out in the general election?" Cruz asked viewers, arguing that Trump's legal problems with his closed university and his financial contributions to Clinton's 2008 presidential campaign would spell huge trouble.

"Nominating Donald would be a disaster," Cruz said.

Trump insisted he was the only one capable of defeating Clinton.

"I have not started on Hillary yet," Trump said. "Believe me, I will start soon."

When Fox moderators pressed Trump on some of his changing political positions on the Iraq war and admitting Syrian refugees, Trump defended his flip-flopping.

"I have a very strong core," he insisted, "but I've never seen a successful person who wasn't flexible."

Trump proceeded to reverse a plank of his own immigration plan, saying he now supports an increase in visas for highly skilled foreign workers.

"I changed my tune," Trump said.

"There's a difference between flexibility, and telling people whatever you need to get them to... do," Rubio interjected.

The debate occurred on a day thousands of conservatives gathered at an annual convention near Washington, with many expressing concerns about Trump.

But House Republican Steve King, who backs Cruz, said forcing a party implosion just to stop a popular candidate was not the answer.

"We should not change the rules just because you don't like the person that emerges in the leadership," King told AFP.