DETROIT (AP) -- Picking up right where they left off, Donald Trump and Marco Rubio traded a new round of insults at the start of the 11th Republican presidential debate Thursday night, and Trump then made a crude sexual reference before the two pledged to try to focus more on policy.
Rubio justified his attacks on Trump by saying the billionaire businessman had "basically mocked everybody" over the past year. Trump countered with a feint, saying he'd called Rubio a "lightweight" in the past but "he's really not that much of a lightweight."
Trump then noted that Rubio had mocked his hands as small, widely viewed as an insult about Trump's sexual prowess, and declared, "I guarantee you, there's no problem" in that area.
Pressed on why he hadn't immediately disavowed David Duke and the Ku Klux Klan when first questioned about it, Trump said he "totally" disavows both.
In advance of the debate, Trump pronounced himself ready for his rivals to bring it on, batting away any suggestion of standing above the fray.
"I can't act overly presidential because I'm going to have people attacking from every side," he said.
With Ben Carson's exit from the race this week, the field of Republican candidates has now been narrowed to four, including Texas Sen. Ted Cruz and Ohio Gov. John Kasich.
But any number of predictions that GOP voters would unite behind one anti-Trump candidate have come and gone without a change in the overall dynamic.
Trump, with 10 state victories, continues to dominate the conversation and the delegate count.
That has GOP establishment figures gnashing their teeth over the prospect that it may soon be too late to stop Trump's insurgent candidacy, and reviving talk of a brokered convention and an irreparably damaged Republican Party.
Mitt Romney, the party's 2012 presidential nominee, on Thursday made a rare public appearance to denounce Trump as "a phony" who is "playing the American public for suckers."
Also publicly criticizing Trump: House Speaker Paul Ryan, who was Romney's running mate, and 2008 GOP nominee John McCain. Ryan said Trump's more controversial ideas "disfigured" conservatism, and McCain voiced concern about Trump's "uninformed and indeed dangerous statements" on national security.
Rubio has been denouncing Trump on both policy and personal grounds as he tries to emerge as Trump's chief rival. He dramatically shifted his tone in the last debate and unleashed a torrent of criticism on Trump. His sparring with Trump deteriorated into a weeklong series of tit-for-tat insults and taunts on everything from bed-wetting to bad tans.
But for all of that, Rubio still came out of Super Tuesday's 11-state round of voting with just one victory, in the Minnesota caucuses.
In advance of Thursday's debate, Rubio signaled his intent to continue his efforts to unmask Trump as a "con artist" who hasn't laid out serious policy proposals.
Turning the nomination over to Trump would mean the "end of the Republican Party," Rubio claimed.
A rejuvenated Cruz, with three Super Tuesday victories to showcase, is insisting that the "the campaign is now down to a two person race - me vs. Donald Trump,"
Cruz is urging his GOP rivals to "prayerfully consider" dropping out of the race to give him a clear shot at the front-runner. Carson may be gone, but Cruz' suggestion to drop out seems to be going nowhere with Rubio and Kasich.
Rubio dismissed Cruz' Super Tuesday trifecta as inconsequential and pinned his own hopes on a March 15 victory in his home state of Florida, which awards all 99 of its delegates to the winner.
Kasich, meanwhile, said it's important to "stop Mr. Trump" and argued that he's the candidate best positioned to do that, by winning his home state of Ohio on March 15.
Speaking to reporters in Detroit in advance of the debate, Kasich said that if he wins Ohio, the Republican primary will likely end with a contested convention in Cleveland.
Thursday's debate, sponsored by Fox News, was the first time Trump faced his rivals since scooping up seven victories on Super Tuesday.
It was also the first time he faced questioning from Fox News' Megyn Kelly since the two clashed in the first primary debate. That's when Kelly's tough questioning about Trump's treatment of women blew up into a running argument between Fox and the candidate. Trump, who dismissed Kelly as a "lightweight" and a "bimbo," ended up boycotting a subsequent Fox debate, claiming the network was unfair.
Trump has continued to pile up delegates during the long, and so far unsuccessful, effort to topple him.
He leads the field with 329 delegates. Cruz has 231, Rubio 110 and Kasich 25. It takes 1,237 delegates to win the Republican nomination for president.
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Benac reported from Washington.
