Republican U.S. presidential candidate Marco Rubio listens as rival candidate Donald Trump speaks at the U.S. Republican presidential candidates debate in Detroit, Michigan, March 3, 2016.
Republican U.S. presidential candidate Marco Rubio listens as rival candidate Donald Trump speaks at the U.S. Republican presidential candidates debate in Detroit, Michigan, March 3, 2016.

Dismissing his rivals as "lying Ted" and "little Marco," Donald Trump fended off intense attacks from his fellow presidential hopefuls at a debate Thursday that comes amid deeps signs of divisions within the Republican Party.

During the debate, Florida Senator Marco Rubio, Texas Senator Ted Cruz and Ohio Governor John Kasich took turns taking swipes at the New York businessman, who appears to be marching toward the party's nomination.

The debate, being held in the northern city of Detroit, was filled with the same yelling, personal insults and off-color remarks that have featured prominently in the 2016 Republican race for president.

Within five minutes of the debate's opening, Trump had seemingly bragged about the size of his genitals.

"[Rubio] said if my hands were small, then something else is small," Trump said, holding up his hands. "I guarantee there's no problem."

Trump was referencing a comment last week made by Rubio that was widely seen as a reference to the businessman's sexual prowess.

FILE - Republican presidential candidates, Sen. Ma
Republican presidential candidates, Sen. Marco Rubio, R-Fla., businessman Donald Trump, Sen. Ted Cruz, R-Texas, and Ohio Gov. John Kasich take the stage before a Republican presidential primary debate at Fox Theatre in Detroit, March 3, 2016.

Rubio keeps up attacks

Over the past week, Rubio has tried to knock Trump off his pedestal by matching him insult for insult. At the debate, Rubio said he would like to discuss policy issues, but he also defended his aggressive strategy.

"For the last year, Donald Trump has basically mocked everybody with personal attacks," Rubio said. "If there's anyone who's ever deserved to be attacked that way, it's Donald Trump."

The bitter Trump-Rubio rivalry continued Thursday, with the ex-reality television star referring to the Florida senator as a "little guy [who] has lied so much about my record."

Rubio fired back: "You ask him a question about the economy and the first thing he does is go into the 'little guy' thing," Rubio said. "And he wants to be president of the United States of America."

Cruz, who had a stronger than expected performance during this week's crucial Super Tuesday nominating contests, took aim at Trump's record, suggesting he had in the past supported Democratic Party candidates over Republican ones.

"Donald Trump supported Jimmy Carter over Ronald Reagan. Donald Trump supported John Kerry over George W. Bush," said Cruz.

Cruz also slammed Trump's vitriolic style. "I think that the American people understand that yelling and cursing at people doesn't make you a tough guy," he said.

Republican presidential candidate, Sen. Ted Cruz,
Republican presidential candidate, Sen. Ted Cruz, R-Texas, argues a point during a Republican presidential primary debate at Fox Theater, Thursday, March 3, 2016.

Trump: Romney a 'failed candidate'

The debate began with a question about someone not on stage: Mitt Romney. The party's most recent nominee strongly criticized Trump in a speech Thursday, calling him a "con man" and a "phony" who is "playing the members of the American public for suckers."

Asked to respond to the criticism, Trump dismissed Romney as a "failed candidate" who was "an embarrassment to everybody" when he lost to President Obama in 2012.

"Obviously he wants to be relevant; he wants to be back in the game," Trump said.

At an earlier news conference, Trump used even more direct language, saying Romney once "begged" for his endorsement during his 2012 presidential run.

"I could have said, 'Mitt, drop to your knees.' He would have dropped to his knees,'" Trump said, in what was widely interpreted as a thinly veiled sexual joke.

Republican split

Trump's bombastic style and often extreme positions have alienated many within the Republican Party, even as he continues to march toward the nomination.

Many Republican lawmakers and leading party figures have said they will never support Trump, even if he is the nominee, while others have begun to coalesce behind him.

It is increasingly unclear what party leaders can do to stop Trump, who has a commanding lead both in national polls and in the count of delegates needed to win the nomination.

Heading into Thursday's debate, Trump is the only Republican candidate on track to win the necessary 1,237 delegates, according to the well-respected Cook Political Report.