New Jersey Gov. Chris Christie on Friday endorsed GOP front-runner Donald Trump, delivering a surprise and powerful boost to the billionaire businessman, whom he called the best Republican candidate to lead the country and beat Democrat Hillary Clinton.

"I've gotten to know all the people on that stage and there is none who is better prepared to provide America with the strong leadership that it needs both at home and around the world than Donald Trump," Christie said at a news conference in Texas. Reporters were visibly stunned when he walked into the room.

"I can guarantee you that the one person that Hillary and Bill Clinton do not want to see on that stage come next September is Donald Trump," said Christie, who dropped his own bid for the presidency earlier this month following a disappointing finish in New Hampshire.

The endorsement, the first for Trump from a sitting governor and a former rival, comes at a particularly opportune time for the real estate mogul, who on Thursday night faced a barrage of new attacks from rival Marco Rubio during the final debate ahead of next week's Super Tuesday contests, where large numbers of delegates are at stake. And it underscored the extent to which Trump has managed to dominate the news cycle and starve rivals of momentum just as they appear to be on the rise.

Rubio hit at Trump's business record, history of hiring foreign workers and his vague policy positions during the debate. The broadsides clearly irritated Trump and threatened to provide Rubio with a jolt of new momentum as he seeks to turn the contest into a two-man race.

Rubio's team had unveiled a flood of endorsements in recent days to cast him as the GOP's preferred alternative to Trump, including nods from the governors from Tennessee, Arkansas and South Carolina.

Christie's move overshadowed them all. "I think this changes the narrative in a dramatic way," said Fred Malek, a major Republican fundraiser.

The timing immediately following the debate, however, appeared to be a coincidence. A former Christie campaign official said the governor made his decision to endorse Trump on Thursday following a meeting in Manhattan attended by the two men and their wives.

Christie was already on a plane heading to Texas as the debate was airing, according to the former official, who was not authorized to speak publically on Christie's behalf and spoke on the condition of anonymity.

While Christie's own campaign for president failed to gain traction in a crowded field, he nonetheless remains a well-regarded figure in the GOP, having served as a top surrogate to 2012 nominee Mitt Romney and as the former chair of the Republican Governors Association.

"Gov. Christie is an enormously respected Republican governor with great credibility," said GOP consultant Phil Musser. "It's a big signal from a major leader in the Republican party."

And indeed, Christie's endorsement was quickly followed by a nod from Maine Gov. Paul LePage, who broke the news in an interview with Howie Carr, a conservative radio talk-show host.

Christie, known as one of his party's most effective and vicious attack dogs, embraced the role within minutes of joining Trump. He slammed Rubio - "Desperate people do desperate things," he said - and shut down a reporter for asking about a lawsuit leveled against Trump.

Trump appeared to relish the attacks, mentioning repeatedly how Christie had "totally destroyed Marco Rubio the other day."

The back-patting was a departure from some of the pair's more heated rhetoric. Before Christie left the race, he questioned Trump's temperament and experience, saying he wasn't suited for the presidency. And after Trump called for a temporary ban on foreign Muslims entering the U.S., Christie said, "This is the kind of thing that people say when they have no experience and don't know what they're talking about."

Christie's re-entry into the race also marks the second time that he has slowed Rubio on the rise. During the last GOP debate before the New Hampshire primary, as Rubio appeared to be on the cusp of a breakthrough, Christie set a verbal trap that left Rubio repeating the same practiced line over and over again.

It was the same tactic Rubio used against Trump in Thursday night's debate, as he forced the billionaire to repeat the same talking points to describe a health care plan thin on detail. "I just watched you repeat yourself five times five seconds ago," Rubio said with glee.

Christie said Friday the decision to endorse Trump was an easy one, as the two men have a longstanding personal friendship. "I absolutely appreciate him as a person and as a friend," he said.

And his options were limited. Christie had long been adamant that first-term senators were not qualified to be president, disqualifying Rubio and Texas Sen. Ted Cruz from consideration, leaving him to choose from Trump, Ohio Gov. John Kasich or retired neurosurgeon Ben Carson. Neither Kasich nor Carson are forecast to be competitive on Super Tuesday.

Christie insisted he and Trump had not discussed potential Cabinet appointments for the former federal prosecutor, who has been floated as a potential vice president, attorney general and secretary of the Homeland Security Department. Instead, he said, he expects to finish out his second term as governor "and then go into private life and make money like Trump."