Mine is bigger than yours: Trump boasts about the size of his manhood then lays into 'Little Marco' as the final four slug it out in bitter Detroit debate 

Donald Trump assured a national television audience on Thursday night that he's not lacking in the manhood department.

Marco Rubio has suggested that Trump has 'small hands,' and that it could indicate another body part could be undersized.

Trump immediately brought it up during a Fox News debate at the Fox Theatre in Detroit.

'He hit my hands. Nobody has ever hit my hands. I've never heard of this one. Look at those hands. Are they small hands?'

'And he referred to my hands – if they're small, something else must be small,' Trump said, recalling a Rubio rally this week as he waved his hands to the audience.

'I guarantee you there's no problem. I guarantee.'

Trump repeatedly referred to Rubio as 'Little Marco' throughout the night.

But he initially retracted another insult he's aimed at the Florida senator.

'He's really not much of a lightweight,' Trump said.

Scroll down for video 

No problem here! Donald Trump began the debate with an incredibly crude reference to the size of his hands as well as his mandhood

The final four: Trump is up against Marco Rubio, Ted Cruz and John Kasich at the debate in Detroit, Michigan. A fifth candidate, Ben Carson, has opted not to attended and is on the verge of suspending his campaign

The bigger man? Trump, who has a wide lead in the Republican delegate count, came out in fighting form, dismissing Mitt Romney and the Ku Klux Klan furore off the bat

Obsessed? Donald Trump is said to repeatedly send Vanity Fair editor Graydon Carter pictures of his hands after he referred to the billionaire businessman as a 'short-fingered vulgarian' in Spy Magazine

Making his point: Mr Trump protested 'He hit my hands. Nobody has ever hit my hands. I've never heard of this one. Look at those hands. Are they small hands?'

Assault from all sides: Donald Trump was forced to field attacks from both Marco Rubio and Ted Cruz, as well as Megyn Kelly the Fox News anchor who challenged him on his flip-flopping political stances

Tag team champs: Trump had to fend off repeated attacks from Rubio (left) and Cruz (right) through the evening, with the best line of the night a joint effort when Cruz told Donald to 'breathe' repeatedly before Rubio finished him off with a joke about yoga

During a February 28 rally in Salem, Virginia, Rubio mocked Trump's hands and drew roars from a crowd of more than 1,000.

'He's always calling me 'Little Marco' ... and I'll admit he's taller than me, he's 6’2″, which is why I don't understand why he has hands the size of someone who's 5'2".

'Have you seen his hands? You know what they say about men with small hands,' Rubio said – adding a pregnant pause.

'You can’t trust them!' he snarked.

After the debate, Trump was happy to address the 'hands' issue again.

'These hands?' he asked a group of reporters in the spin room.

'Look at these hands!' he said as he turned them back and forth and stretched out his fingers for effect.

'These are the hands that can rip a golf ball 285 yards,' Trump said, gripping an imaginary driver.

He motioned to a television reporter – a tall, burly man from the entertainment program 'Extra' – and asked him to put his hand up against his own.

The Donald's fingers were fatter but longer.

'See? Look! Hah! My hands are fine,' he said, triumphantly as his wife Melania looked away.

She stood next to him throughout the exchange.

'And the other thing, I can tell you, it's fine,' Trump said before moving down the rope line for another interview.

Trump blasted Rubio during the debate as a 'con artist' – turning that epithet back again its originator – as he said he was an absentee senator.

'He doesn't vote! He doesn't show up to work!' Trump said.

'He defrauded the people of Florida! You defrauded the people, little Marco.'

At the end of the night all four candidates on stage pledged that they would support the eventual Republican nominee.

'Even if it's not me?' an incredulous Trump asked, before declaring: 'Yes, I will.'

Megyn Kelly, the Fox News anchor who famously sparred with Trump during the first GOP debate in August, was cordial to him on Thursday but kept him on task.

She played video excerpts of televised interviews where Trump contradicted himself on sending American troops into Afghanistan, accepting Syrian refugees into America and the question of whether or not President George W. Bush lied drag America into the Iraq War.

'I have a very strong core,' Trump shot back, but 'I've never seen a successful person who wasn’t flexible, who didn’t have a certain degree of flexibility.'

'You have to be flexible, because you learn,' he said as cheers erupted.

Kelly also grilled Trump on class-action lawsuits targeting his 'Trump University' real estate seminars.

'We have a 98 per cent approval rating, we have an A from the Better Business Bureau and people like it,' Trump said of the now-defunct project.

'The rating from the BBB was a D-minus,' Kelly shot back.

'There’s a class action of 5,000 people' including veterans and teachers,' she said, who felt 'fleeced' by the classes.

You can't be serious! Thursday night's debate was characterized by frequent character attacks among the three leading candidates, while John Kasich remained above the fray

Vying for second place? The early exchange seemed to go over the head of Ted Cruz, who has the second highest number of Republican delegates so far and is trying to position himself as the only candidate who can beat Trump

Disavowed: As well as defending his manhood from Rubio, Trump was forced to speak about his feud with Mitt Romney and thoughts on the Ku Klus Klan early on in the debate

The bigger man: Trump repeatedly referred to Marco Rubio as 'Little Marco' throughout the night although he initially retracted another insult he's aimed at the Florida senator that he is a 'lightweight'

He's a con artist! Trump later blasted Rubio with the same insult used on him, saying he was an absentee senator who 'doesn't vote and doesn't show up to work'

'I'm a leader, I've always been a leader': Trump insisted he has never had any problem leading people

Trump also took shots at Texas Sen. Ted Cruz, calling him 'Lying Ted' when he was challenged about an off-the-record editorial board meeting he held with the New York Times.

Trump reportedly suggested in that meeting that he might soften his rock-ribbed immigration positions and was taking a hard line as a way to start a later negotiation.

Cruz suggested he was 'lying to the American people' about what he would do as president.

'You're the lying guy up here. You're the liar, lying Ted,' Trump fired back.

That hammer blow came after weeks of wrangling over Cruz's alleged dishonesty to advance his campaign in Iowa, and Trump's complaint that the Texas had misrepresented his positions on Obamacare, guns and immigration.

As Trump sparred with Cruz on his use of foreign workers at his Palm Beach hotel, Cruz tried to put The Donald into a time out.

'Learn not to interrupt, Donald. It's not complicated. Count to ten. Count to ten,' he lectured.

Cruz later said in an exchange about his support for the nomination of Chief Justice John Roberts that 'Donald has a tenuous relationship with the truth.'

Trump jumped into the breach again, and Cruz was ready for him.

'Breathe. Breathe. Breathe,' he mocked.

Trump sniped back: 'Lying Ted!'

And Rubio piped up: 'When they're done with the yoga, can I answer the question?'

'He's very flexible,' Rubio said of Trump's admission that his positions were malleable, 'so you never know.'

Breathe Donald: Cruz later said in an exchange about his support for the nomination of Chief Justice John Roberts that 'Donald has a tenuous relationship with the truth' but when Trump jumped into the breach again, Cruz was ready for him.

'Learn not to interrupt... count to 10': Cruz had a particularly memorable line when trying to put Trump in his place during one of their several frosty exchanges

'Lying Ted': Trump also took shots at Texas Senator Cruz, when he was challenged about an off-the-record editorial board meeting he held with the New York Times

Cruz suggested he was 'lying to the American people' about what he would do as president;'You're the lying guy up here. You're the liar, lying Ted,' Trump fired back

As Trump sparred with Cruz on his use of foreign workers at his Palm Beach hotel, Cruz tried to put him in a time out. 'Learn not to interrupt, Donald. It's not complicated. Count to ten. Count to ten'

The billionaire was forced to defend his position on waterboarding and other enhanced interrogation techniques after former CIA director Michael Hayden warned that U.S. personnel might disobey a President Trump's orders.

'They won't refuse. They're not going to refuse me. Believe me,' Trump vowed.

'You look at the Middle East, they're chopping off heads, they're chopping off the heads of Christians and anybody else who happens to be in the way, they're drowning people in steel cages and now we're talking about waterboarding?'

'I'm a leader, I've always been a leader. I've never had any problem leading people,' Trump insisted.

'If I say do it, they're going to do it. That's what leadership is all about.'

Thursday's debate was the 11th in a series of smackdowns that began in August with 17 candidates spread out over two events on a single day.

But now just five remain, and one – retired surgeon Ben Carson – decided not to show up in Detroit.

Confusion reigns over the question of whether Carson will stay in the presidential race at all. But he wasn't on the debate stage.

Rubio and Cruz, meanwhile, are jockeying for position, hoping to emerge as the default anti-Trump contender

Trump also took a shot at 2012 Republican presidential nominee Mitt Romney, who hammered him in a morning speech as a 'phony' who would lead the GOP to ruin if he is the part's standard-bearer in November.

Trump called him a 'failed candidate' during an afternoon rally in Portland, Maine, and said Romney had 'begged' him for an endorsement four years ago.

'I guess he wants to be relevant,' Trump scoffed during the debate.

'He wants to be back in the game.'

Trump is leading the field in national polls, in primary delegates to the Republican National Convention, and in the numbers of states he has won.

Of the 15 states that have held primaries or caucuses, Trump has prevailed in 10.

'CNN just came out with a poll two days ago, a national poll ... where he's at 15,' Trump said, pointing at Rubio.

Need any water, Marco? The candidates talk during a commercial break after going at each other's throats non-stop through the debate

Next to go? John Kasich, who is in fourth place in polls, is attempting to position himself as the 'adult in the room'

How do you think it's going, Ted? John Kasich, the Governor of Ohio, and Texas Senator Ted Cruz share a joke during a commercial

Fist bump: Despite the fractious back and forth through the evening, the candidates were able to bump fists at the end of the night in after finishing the night saying they would back one another were they to become the nominee

Family support: After an evening of attacks, Trump, while being interviewed by Bill O'Reilly, was joined on stage by his wife Melania (pictured right in the blue dress, and his son Eric

Frosty: During the frosty exchange, Mr Trump accused O'Reilly of going negative on him, accusing him of getting 'carried away'

Friends reunited: Megyn Kelly, center, appeared in the same room with Donald Trump for the first time since their infamous run-in; Kelly said she was not anticipating any more fights with Trump

Waiting to pounce: Kelly did not ask Trump a question for the first 30 minutes of the debate but eventually honed in on him, asking about his political stances and lawsuits filed against him and Trump University

'He's at 14,' he added, nodding at Cruz, 'and I'm at 49.'

More pressing, however, is the question of which Republican White House hopeful could beat Hillary Clinton in a general election.

Clinton, the former U.S. secretary of state, is the presumptive Democratic nominee.

'Of all the people on this stage,' Rubio claimed Thursday night, Trump 'performs the worst against Hillary Clinton.'

'Wrong!' Trump boomed.

'I beat Hillary Clinton! I beat Hillary Clinton in many polls.'

Rubio jumped in to disagree, but Trump was having none of it.

'Excuse me!' he yelled. 'I think I'm talking!'

'I beat Hillary Clinton in many polls. The Pew poll just came out. I beat Hillary Clinton in a recent Fox poll, I beat Hillary Clinton in USA Today. I beat her today in a poll in Ohio.'

'I'm the only one who beats Hillary Clinton,' he claimed.

'I have not started on Hillary yet, believe me ... I haven't even started.'

The debate came after hundreds of protesters gathered outside the theater in the snow. Most of the group were protesting the water crisis in nearby Flint, just an hour north of Detroit, holding signs that read 'Flint Lives Matters' and calling for the resignation of Governor Rick Snyder.

They were not the only group protesting though, with a large number of people also calling for a national minimum wage of $15 an hour outside the venue as well.

Mudslinging: The lead-up to the debate was dominated by a furious back-and-forth between Mitt Romney (pictured on Thursday in Salt Lake City) and Donald Trump after the 2012 Republican Presidential candidate said his party should select anyone else as their nominee 

Rapturous audience: The crowd stands and watches the Republican presidential candidates trade blows on the stage

Packed house: The four candidates locked horns for the 11th time in front of thousands inside the ornate hall of the Fox Theatre

Ready to rumble: The showdown took place at the historic Fox Theatre, a 5,000 capacity venue first opened in 1928; it was designated a National Historic Landmark in 1989

Full of hot air? A protester holds a pinata of his likeness outside the Fox Theatre; earlier Mr Trump described Mitt Romney as a 'failed candidate' who delivered an 'irrelevant' speech and would have done anything to secure Trump's endorsement

A storm brewing: Protesters gather outside of Fox Theatre in Detroit before the Republican presidential debate kicked off to highlight police brutality and the number of people killed by cops this year alone

Flint lives matter: Michigan's residents are using the debate to highlight the problem with Flint's water. Protesters believe that Republicans in the Senate have been silent on the scandal

Clear message: A protester braved the elements to shout slogans outside the Fox Theatre ahead of the debate. Flint demonstrators want a Republican response from candidates and its party

Not just Romney then: As well as Flint and Black Lives Matter demonstrations, there was a noticeable contingent unhappy with the Republican front runner, calling on the party to Dump Trump

Friends of Romney? This demonstrator appears to have taken Mitt's message on board after the 2012 candidate described Trump as a boorish know-nothing who will hand the presidency straight to Hillary Clinton

Come get my vote: Fast food workers advocating for a $15 minimum wage  and the right to form a union without retaliation also took the opportunity to march in front of the cameras ahead of the big show

The devil's in the detail: The group took a shot at the much-maligned governor Rick Snyder, who is under severe pressure following the Flint water crisis and his response to it

Standing together: The group wants billion dollar companies to pay their employees better so they can make ends meet and as they put it 'rebuild the middle class and get the economy working again'