New Jersey Gov. Chris Christie, right, introduces Donald Trump Friday after endorsing him before a rally at the Fort Worth Convention Center in Fort Worth, Texas.

New Jersey Gov. Chris Christie has a reputation for vengeance.

And he delivered it with gusto on Friday as he shocked many in the political world by endorsing GOP front-runner Donald Trump for the Republican presidential nomination.

The surprise endorsement, the first for Trump from a sitting governor and by far his most prominent, comes as Trump rival Marco Rubio appeared on the cusp of a breakthrough following a break-out debate performance. And it marks the second time that Christie has knee-capped the Florida senator, just as he appeared to be on the rise.

At the news conference in Fort Worth, Texas, Christie described Trump — a man he had previously panned as ill-suited for the White House — as 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. Reporters covering the event were visibly stunned when the governor, who dropped his own bid for the presidency earlier this month following a disappointing finish in New Hampshire, walked into the room.

The endorsement comes at a particularly opportune time for the real estate mogul, who on Thursday night faced a barrage of new attacks from Rubio during the final debate ahead of next week’s Super Tuesday contests, where large numbers of delegates are at stake. It was the second time Christie has managed to tear down Rubio just as he was on the rise. During the last GOP debate before the New Hampshire primary, as Rubio appeared on the cusp of a breakthrough, Christie set a verbal trap that left Rubio repeating the same practiced line over and over again.