Gov. Chris Christie says he first met Donald J. Trump 14 years ago as a courtesy to Judge Maryanne Trump Barry, after she told him, “My little brother really wants to meet you.”  Mr. Christie had just become the top federal prosecutor in New Jersey. Mr. Trump owned casinos in Atlantic City, where it makes sense to have friends in law enforcement. But Mr. Christie left friends and associates with the impression that he was just as eager to meet Mr. Trump.  He began referring to Mr. Trump as “a friend of mine,” the way he later would Jerry Jones, the owner of the Dallas Cowboys, whose private plane and private box he enjoyed; King Abdullah, who hosted him on a lavish weekend in the Jordanian desert; Bono, the singer of U2, who joined them at parties there; and, after a long period of unrequited adulation, Bruce Springsteen. Much like Mr. Trump, Mr. Christie had shown that he liked to be around People Who Matter.  That request for a meeting from a big sister started a curious friendship of convenience — some call it deeply transactional — that led to Mr. Christie’s surprise endorsement of Mr. Trump last week in the Republican presidential race.  In a news conference in Trenton, Gov. Chris Christie addressed calls for him to resign, his support for Donald J. Trump and his appearance at a recent Trump news conference.  The endorsement could be their ultimate transaction: Mr. Trump, having seized Mr. Christie’s position as the tell-it-like-it-is candidate in the Republican primary, is in a fierce fight to lock up the nomination. Mr. Christie, a term-limited governor estranged from his state after spending most of his second term away from it, is looking to extend his relevance.  Mr. Christie defended himself against the blowback — the Internet ridicule and denunciations from his financial backers, the calls for his resignation from the New Jersey Republicans who had once jumped at his command. At a news conference on Thursday, he said that he could govern his state and campaign for Mr. Trump at the same time, and scoffed at the reaction to his stand-by-your-man appearance beside Mr. Trump on Super Tuesday: “I wasn’t being held hostage.”  Those who know both Mr. Christie and Mr. Trump describe them as alike in many ways: Polarizing and self-regarding, each can summon the charm to make an acquaintance feel like the only person in the room, and just as quickly turn if a relationship no longer suits his interests. Mr. Trump is The Donald; Mr. Christie’s re-election slogan was “The Governor.”  “They both have very immense egos; they both sort of have the feeling that they have the power to do anything,” said Alan Steinberg, who served in the administrations of Gov. Christie Whitman and President George W. Bush. (Mr. Steinberg supported Mr. Christie for governor but now backs Senator Ted Cruz of Texas for president.)  “They think they can just bully their way through,” he added. “They both skirt the edge; they both have tendencies toward mendacity. It’s the perfect bromance.”  Mr. Christie has told audiences variously that it was during a face-to-face meeting or on a phone call that Judge Barry, with the United States Court of Appeals for the Third Circuit, in Newark, asked him to meet her brother in 2002.  Mr. Christie was relatively new to public life, and eager for it; he had been a Morris County freeholder, but failed in his campaigns for higher office and was appointed federal prosecutor after his brother, Todd, donated handsomely to Mr. Bush’s first presidential campaign.  Mr. Trump had long worked Atlantic City politics to suit his casino interests, but he had just lost a fight against a tunnel project that would serve a casino proposed by his longtime archrival, Steve Wynn; Mr. Trump called the tunnel “Steve Wynn’s private driveway.” Mr. Wynn now supports Mr. Trump for president.  Mr. Christie and Mr. Trump met over dinner at Jean-Georges, the celebrity-chef restaurant in one of Mr. Trump’s towers on the West Side of Manhattan. Mr. Christie recalled Mr. Trump’s ordering for him when the chef, Jean-Georges Vongerichten, came out to greet him. (“The special thing you made for me? We’ll take two of those, too. ”)  Three years later, Mr. Christie’s friends in New Jersey were impressed when he was invited to Mr. Trump’s third wedding, in Palm Beach, Fla.  “That was kind of a who’s who,” said State Senator Joe Kyrillos, a longtime friend of Mr. Christie who as the New Jersey Republican Party chairman helped him become a United States attorney, but supported Jeb Bush for president after a falling out with Mr. Christie. “I recall Hillary was there, too.” (The other most prominent New Jersey face among the crowd was George Norcross, a Democratic power broker often described as the most powerful nonelected person in the state, who was then a frequent golf partner of Mr. Trump’s and later helped Mr. Christie win and govern in a blue state.)  Republicans were equally surprised to see Mr. Trump in the third row of a Newark basilica for the Mass before Mr. Christie’s inauguration in 2010. (Mr. Trump was not a stranger to New Jersey governors and their inaugurations; when Barry Manilow canceled a plan to play at Governor Whitman’s inauguration party in Atlantic City at the last minute, Mr. Trump prevailed on Paul Anka to fill in.)  Of course, any highly public relationship like the one between Mr. Trump and Mr. Christie can make for awkward situations. As United States attorney, Mr. Christie went after Charles Kushner, a real-estate developer and major New Jersey political donor who pleaded guilty in 2005 to tax evasion and making illegal campaign contributions — and four years later became the father-in-law of Mr. Trump’s daughter Ivanka.  But by 2010, Mr. Trump was then battling with another rich New Yorker, Carl Icahn, to win back control of his Atlantic City casinos after they entered bankruptcy. He won a month after Mr. Christie’s inauguration. A year later, the governor, Mr. Trump and their wives landed on Page Six, in The New York Post, after another dinner at Jean-Georges. Mr. Icahn became a backer of Mr. Trump for president; Mr. Trump suggested he might appoint him Treasury secretary.  Mr. Trump made a larger-than-usual donation, of $250,000, to the Republican Governors Association in 2014, when Mr. Christie led it. Mr. Kushner, too, has held at least one event for Mr. Trump at his home on the Jersey Shore.  “It started out professional, but I think it’s definitely evolved into a more personal relationship,” Dale Florio, a longtime Republican fund-raiser in New Jersey, said of the Trump-Christie connection.  Others who know the two men describe their alliance more as an acquaintanceship, as many of Mr. Trump’s relationships are. His true friendships are limited to the small number of people he plays golf with in Palm Beach or at Trump National Golf Club Bedminster, which he created from the former estate of John DeLorean, the flamboyant auto industry executive, in the heart of New Jersey horse country. (Mr. Christie is not a golfer.)  Once they started to compete to be the Republican nominee, the friendship strained.  As Mr. Trump surged in the polls, one New Jersey political leader, who like many people interviewed for this article did not want to be identified out of fear of reprisals from either man, said he had urged Mr. Christie to directly confront Mr. Trump, saying he was the only candidate who could do it. Mr. Christie did not disagree, this person said, but “he was afraid to do it — he’s never been afraid of anybody.”  “He thought Trump would do to him what he did to Megyn Kelly,” this person continued, referring to the Fox News anchor Mr. Trump relentlessly demeaned because he did not like her questions in an early debate.  Mr. Trump, however, did not hold back. He declared that Mr. Christie “totally knew” about the lane closings at the George Washington Bridge that were engineered to punish a perceived political enemy, and that the governor could never win the nomination given his dive in popularity and his record in New Jersey.  But after Mr. Christie dropped out following his fifth-place showing in the New Hampshire primary last month, he told allies he appreciated that Mr. Trump had called him that very night. The two men had a long talk.  Six days after he dropped out, Mr. Christie told about 40 guests gathered over coffee and cookies before his budget address that he did not see a path to the nomination for anyone but Mr. Trump.  Still, on a phone call two days later, he told the state’s Republican Party county leaders to “keep their powder dry” when it came to endorsements, in the words of one person on the call.  A week later, he and his wife had breakfast with Mr. Trump at Trump Tower, in Manhattan. The governor jumped at the chance to go to Texas to endorse his former rival.  “He would not have done this unless he thinks that the only path forward for him is with Trump, and that Trump is going to win,” said a high-ranking Republican, referring to the governor.  Mr. Trump, standing next to Mr. Christie in Texas last month, said, “Generally speaking, I’m not big on endorsements. This was an endorsement that really meant a lot.”  At his news conference on Thursday, Mr. Christie said that he had “no current plans” to go on the road with Mr. Trump again. Still, he remained unbowed.  “If he had not been in the race,” he said, “I would have been the nominee.”
Starting with a dinner in 2002 that Mr. Trump’s sister set up, he and the New Jersey governor established a relationship that led to an endorsement.