Republican presidential contenders Mitt Romney and Newt Gingrich clashed repeatedly in heated, personal terms in the first campaign debate since South Carolina's primary scrambled the race to pick a challenger to President Barack Obama.
Mr Romney, the former Massachusetts governor, branded his chief rival as an "influence peddler" in Washington, only to be accused in turn by Mr Gingrich, the former speaker of the House of Representatives, of spreading falsehoods over many years in politics during a two-hour debate marked by interruptions and finger pointing.
Mr Gingrich has suddenly seized the nomination momentum, following weak finishes in the first two contests in Iowa and New Hampshire, with his solid victory on Saturday over Mr Romney in South Carolina.
Recent polls suggest he may have erased Mr Romney's once double-digit lead in Florida, site of the next primary on January 31.
Mr Romney remains the favourite of much of the Republican establishment and has a big advantage in money and organisation.
Florida is also seen as friendlier territory for him than South Carolina, one of the most conservative states.
But the South Carolina win has allowed Mr Gingrich to position himself as the only viable alternative to Mr Romney, whom some Republicans see as too moderate.
The two other candidates remaining in the race, former Pennsylvania Senator Rick Santorum and Texas Representative Ron Paul, shared the debate stage, but are seen as long-shots for the nomination.
The debate came one night before Mr Obama's nationally televised State of the Union policy speech to Congress offering him his biggest, best chance to offer a vision for a second term in a year dominated by Republican infighting.
Mr Obama will speak to a nation worried about daily struggles and unhappy with his handling of the economy. The president is expected to urge higher taxes on the wealthy, propose ways to make college more affordable and offer new steps to tackle a debilitating housing crisis and try to help US manufacturers expand hiring.