NEW YORK - Marco Rubio, a first-term United States Senator on the rise in the presidential race, faced a barrage of attacks in Saturday night's Republican debate, with rivals vigorously challenging his preparedness to be president and the depth of his expertise as they sought to salvage their own White House hopes.

The governors running in the mainstream conservative lane - Jeb Bush, Chris Christie and John Kasich - are fighting for their political lives. All three need a second place finish behind Donald Trump, the front-runner in the state, to carry on.

The need to score a top spot was evident, particularly from Christie, who went on the offensive early and often and never missed an opportunity to flip a question into an attack against Rubio, who came in third place in the Iowa caucuses, just one point behind second place Trump. During the Saturday debate at Saint Anselm College in Manchester, New Hampshire, Rubio, the 44-year-old Florida senator,  was portrayed as too inexperienced for the White House. Christie savaged Rubio for being a senator, saying all he thinks about when he wakes up is what kind of speech to give or bill to drop.

 He hit back at one of the accomplishments attributed to Rubio - the passage of the Hezbollah Sanctions Act - saying the Florida Republican missed the vote for a bill he has bragged about being instrumental in passing. “That’s not leadership, that’s truancy,” Christie said. "You have not been involved in a consequential decision where you had to be held accountable," Christie said looking towards Rubio. "You just simply haven't."

In response, Rubio criticized Christie for his character and integrity. "Chris, your state got hit with a massive snowstorm two weeks ago; you didn't even want to go back. They had to shame you into going back," Rubio said with the crowd booing him. He said that "the experience is not just what you did but how it worked out. Under Chris Christie's governorship of New Jersey, they've been downgraded nine times in their credit rating."

Sen. Rubio has sought to appeal both to mainstream Republicans and those eager to upend the status quo. Senator Ted Cruz, fresh off his victory in the Iowa caucuses, also came under withering criticism for controversial political tactics, with one candidate disparaging him for having "Washington ethics" and being willing to test the campaign's legal limits.

The focus on the two senators allowed Republican front-runner Donald Trump to go largely untouched in his return to the debate stage. His grip on the Republican lead has been shaken by his second-place finish in Iowa, though the next contest Tuesday in New Hampshire is still his to lose. Former Florida Governor Jeb Bush compared Rubio's experience in the Senate with that of President Barack Barack Obama, who also was a first-term senator when he took office. By electing Obama, the United States got "soaring eloquence," but few results, he noted.

Donald Trump clashed with Jeb Bush over the use of eminent domain to seize private lands for projects for the public good. Trump called eminent domain "a good thing," saying, it was necessary to constructing roads, bridges, schools and hospitals. "Certainly, it's a necessity for our country."However, Bush said Trump used “eminent domain to try to take the property of an elderly woman on the strip in Atlantic City. That is not public purpose. That is downright wrong."

Polls show Trump leading in New Hampshire, which is the second of the state-by-state nominating contests to select candidates in the Nov. 8 election. Rubio is catching up fast after an astonishingly strong third-place finish on Monday in Iowa, behind US Senator Ted Cruz and Trump. Trump, unlike previous Republican debates, was not the centre of attention on social media during the debate on Saturday. Rubio had the highest share of conversations on Twitter with 25 percent as of midway through the debate. He was followed by Trump and Cruz at 22 and 19 percent respectively.