US election 2012: Mitt Romney asserts his authority over Newt Gingrich in Florida debate

Mitt Romney asserted his authority over Newt Gingrich in a Republican presidential debate on Thursday night, aggressively turning the former House Speaker's own attacks against him in advance of the crucial primary election in Florida.

The former Massachusetts governor, who over the past 48 hours has pushed back a surge in support for Mr Gingrich across the state, overpowered his rival during bitter disputes over immigration policy, personal finances and the former Speaker's proposal to build a colony on the moon.

After losing the South Carolina primary last weekend, Mr Romney is seeking to stabilise his campaign to be the Republican candidate to face President Barack Obama in November. Florida is the biggest state to vote in the party contest so far and is expected to be crucial in the general election.

He hit out at Mr Gingrich in the 19th debate's opening minutes for describing him as “anti-immigrant”, calling the attack “simply inexcusable”. He pointed out that Marco Rubio, the Cuban-American Florida senator, had backed him and called the criticism “inexcusable and inflammatory”.

Mr Romney has proposed that America's 11 million illegal immigrants “self-deport”. “Mr Speaker, I'm not anti-immigrant,” he said. “My father was born in Mexico, my wife's father was born in Wales. They came into this country. The idea that I’m anti-immigrant is repulsive.”

An animated Mr Romney drove the point home by saying that Mr Gingrich's remarks were “the kind of over-the-top rhetoric that has characterised American politics for too long”.

Speaking in one of the states most affected by the US housing market meltdown and financial collapse, Mr Romney also got the better of Mr Gingrich in a row over Freddie Mac, the government-backed mortgage lender that had to be bailed out for tens of billions of dollars.

Mr Gingrich was paid $1.6 million (£1 million) as a “consultant” to the firm. “Fannie Mae and Freddie Mac were a big part of why we have the housing crisis in the nation that we have,” said Mr Romney. “Speaker Gingrich was hired by Freddie Mac to promote them ... throughout Washington”.

The former Speaker retorted that Mr Romney had investments in funds that held stock in Fannie Mae and Freddie Mac, but Mr Romney simply pointed out that Mr Gingrich did as well, leaving the former Speaker almost speechless. “To compare my investments with his is like comparing a tiny mouse with a giant elephant,” he eventually said.

Mr Romney’s strong showing appeared to demonstrate a return to confidence, underpinned by a series of new polls this week that placed him five points clear of Mr Gingrich in the race to win Florida.

The gathering momentum for Mr Romney ahead of next Tuesday’s vote is a major disappointment from Mr Gingrich, who now looks to have failed to sustain his own surge after scoring a spectacular win in South Carolina. Victory in Florida, which hands 50 delegates to the winner, would represent a major step forward for Mr Romney in his race to win the nomination.

Mr Gingrich was also ridiculed for his proposal earlier this week to establish an American colony on the moon. "If I had a business executive come to me and say they wanted to spend a few hundred billion dollars to put a colony on the moon, I'd say, 'You're fired'," said Mr Romney, who felt confident enough to use a phrase previously seen as toxic to his candidacy.

The former Speaker's bad night was compounded by a strong performance from Rick Santorum, the former Pennsylvania senator and a favourite of the religious Right, who could dent Mr Gingrich's support on Tuesday. Mr Santorum again put Mr Romney under pressure for the health care plan he implemented as governor of Massachusetts, which became the basis for Mr Obama's national scheme.

As his miserable night continued, Mr Gingrich resorted to requesting a “truce” with Mr Romney. Given an opportunity to repeat a criticism of Mr Romney's low personal tax rate that he has been making all week on the campaign trail, Mr Gingrich dismissed the suggestion as “a nonsense question”.

He then changed his mind, stating: “I don't know of any American president that has ever had a Swiss bank account”. But by then Mr Romney – who remarked it would be “nice if people didn't make accusations somewhere else that they weren't prepared to defend here – had won the argument.

After the debate, Mr Romney appeared to claim a victory for himself after a positive reaction from an audience that had cheered several of his answers. “I think it was a big step forward and it is going to give me the boost I need going into this primary,” he said.

Even R.C. Hammond, a spokesman for Mr Gingrich, appeared unable to disguise his boss's poor showing. Asked who had won the debate, he replied: “It was a push – I think Rick Santorum had a good night”.

Ron Paul, a 76-year-old Texas congressman and former doctor, provided a moment of humour when asked if he was prepared to release his medical records to prove he was fit enough to serve as US president.

"Oh, obviously, because it's about one page, if even that long," he said, adding: "I'm willing to challenge any of these gentlemen up here to a 25-mile bike ride any time of the day in the heat of Texas".