Chris Christie Once Mocked Donald Trump for 'You're Fired' Fame — Now He's Endorsing Him

New Jersey Governor Chris Christie endorsed Donald Trump for president today, signaling the first real establishment backing for the Republican frontrunner as the party grows increasingly worried about the possibility of him winning the nomination.

"I am proud to be here to endorse Donald Trump for president of the United States," Christie said at a press conference in Texas Friday afternoon.

"The best person to beat Hillary Clinton on that stage last night is undoubtedly Donald Trump," Christie added, referencing Thursday night's GOP debate.

This is Trump's first endorsement from a sitting governor and a major Republican leader. Christie was also the chair of the Republican Governor's Association, one of the party's campaign organizations, in 2014.

This is huge. It is a 'respectable' Trump endorsement. It'll open the gates. Saves Trump's awful news cycle. Don't kid; this is a big deal.

— Noah Rothman (@NoahCRothman)February 26, 2016

"It is my great honor to receive the endorsement of the Governor," Trump said. "We have had a wonderful relationship for many years. He is a solid person that I have tremendous respect for."

Related: Decisive Win for Trump in Nevada Means Soul Searching for Cruz and Rubio

Trump himself acknowledged that he "was not big on endorsements" but Christie's endorsement "really meant a lot."

Christie's endorsement was followed just a few hours later by one from Maine Gov. Paul LePage, who said in a radio interview that he too is backing Trump for president. LePage previously supported Christie for the nomination.

"The one thing I like about Donald Trump, I'm not gonna say I agree with everything he's saying… he's showing a vision for the future," LePage said, according to the Guardian. "He wants to make America great again, and he's the only person doing that right now."

Christie, who has said many times that he considers Trump a friend, rarely attacked the frontrunner while he was campaigning for the presidency -- despite calls from party members to do so. Christie instead focused his attacks largely on Sen. Marco Rubio, the candidate he saw as most directly blocking his path to the White House.

But Christie's relationship with Trump wasn't always friendly. In January, Christie made fun of the Republican frontrunner during a campaign rally in Iowa.

"Let's not send somebody to the White House whose only experience is being in a fake boardroom in New York City looking into a camera and saying, 'You're fired,' " Christie said, referencing Trump.

He also mocked Trump for skipping a debate over his acrimonious relationship with Fox News, comparing the candidate to a teenager and questioning whether Trump would also "go upstairs to the residence and say I'm not playing" when attacked by Vladimir Putin or Hillary Clinton.

Related: Trump Wins Nevada Amid Hijinks, Confusion and Voter Fraud Allegations

Trump, meanwhile, has dished it back to Christie. Last December, Trump went after the governor for his cooperation with President Barack Obama during the aftermath of Hurricane Sandy.

"When I saw it, I said I think he's going to vote for Obama," Trump said. Trump then went on to call Christie "a little child" and questioned his abilities as governor.

How is Chris Christie running the state of NJ, which is deeply troubled, when he is spending all of his time in NH? New Jerseyans not happy!

— Donald J. Trump (@realDonaldTrump)November 30, 2015

But Christie and Trump do have several things in common — besides their thick tri-state accents. Both are known for speaking their minds and using colorful language even when it's unpopular, a tactic that has proved popular with the Republican electorate during this election.

But both also seem to take huge enjoyment in attacking Rubio. During a now-infamous debate in New Hampshire three weeks ago, Christie unleashed on the junior Florida senator in New Hampshire for reciting the same memorized talking point over and over again. The attack ended up being damaging enough for Rubio that he never really recovered and ended up coming in fourth place in the primary.

Related: Trump and Cruz Attack Each Other in Nevada, Give Rubio a Free Pass

Trump continued where Christie left off pulverizing Rubio during today's press conference.

Rubio is "not presidential material," said Trump. "I've never seen a human being sweat the way this man sweats."

In case it wasn't clear that he thinks Rubio is weak, Trump also called him a "nervous nelly," and a "total mess."

"I watched Chris do a number on him," Trump said laughing, turning to Christie, who smiled. "I've never seen someone melt down like that"

Lightweight Marco Rubio was working hard last night. The problem is, he is a choker, and once a choker, always a choker! Mr. Meltdown.

— Donald J. Trump (@realDonaldTrump)February 26, 2016

Trump declined to say if he was going to tap Christie as his running mate, only saying that they haven't discussed the topic but "he's certainly got the talent"

Christie also demurred, saying that he doesn't "speculate on those kind of things."

But the speculation began even before Christie's endorsement shocked the political establishment, including the possibility that Trump could name him attorney general. Before becoming governor, Christie served as the US Attorney for New Jersey.

Christie dropped out of the presidential race after a disappointing sixth finish in the New Hampshire primary. His endorsement for Trump comes just days before Super Tuesday on March 1, in which eleven states will hold their primary elections. Approximately one-quarter of Republican delegates will be distributed on Tuesday and Trump is overwhelmingly favored in those contests. Today's endorsement could boost Trump's standing even more.

VIDEO: Trump's Faithful Televangelists (Extra Scene from 'TrumpCarolina')/VICE News.

Update: This story has been updated to include Maine Gov. Paul LePage's endorsement of Trump on Friday.

Follow Olivia Becker on Twitter: @obecker928.