MANCHESTER, N.H. -- Days of Gov. Chris Christie's consistent snipes at U.S. Sen. Marco Rubio hit a boiling point Saturday night with a five-minute fiery exchange between the two on the eighth Republican presidential debate stage in New Hampshire.

Christie, who's been losing ground in the early-voting state he's pinned his presidential hopes ahead of Tuesday's primary, launched an aggressive attack against the Florida senator just as soon as he was given an opportunity to speak. The battle was a clear highlight of the debate's first hour.

"You have not been involved in a consequential decision where you need to be held accountable," Christie fired at Rubio, accusing him of "truancy" for missing votes in the Senate.

Christie warned voters here against supporting another first-term senator as the country did with President Obama in 2008. He argued Rubio, like Obama, is simply "not ready to be president of the United States."

In response, Rubio challenged Christie on his economic record in New Jersey. But Christie was ready to fire back.

"I want the people at home to think about this. That is what Washington, D.C. does. The drive by shot at the beginning with incorrect and incomplete information and then the memorized 25 second speech that is exactly what his advisers gave him," Christie said.

Later, Christie argued it was "abundantly clear" Rubio didn't fight for immigration legislation he supported on the floor of the U.S. Senate.

"The fact of the matter is a leader should fight for what they believe in," said Christie, arguing he's a fighter.

With time running out and his poll numbers slipping, Christie shifted gears this week and has gone into full attack mode against Republican rivals he's trailing.

The governor who resisted the urge to attack GOP rivals and instead focused on Democrats Hillary Clinton and President Obama has been replaced by a candidate who needs no urging to go on the offensive against his competition.

Christie's final push here has been dominated by scathing critiques of Rubio and forceful dismissals of Florida Gov. Jeb Bush and Ohio Gov. John Kasich, both widely considered Christie's chief rivals.

The GOP Debate in Manchester, NH 37 Gallery: The GOP Debate in Manchester, NH

Matt Arco may be reached at marco@njadvancemedia.com. Follow him on Twitter @MatthewArco or on Facebook. Follow NJ.com Politics on Facebook.