Chris Christie - the brash New Jersey governor whose fast rise in Republican politics was undone by a petty scheme to clog traffic on a bridge - suspended his presidential campaign yesterday, saying that his standing in the polls was "just not enough" to justify soldiering on.

Christie finished sixth in Wednesday's primary in New Hampshire, the state on which he had pinned his last presidential hopes. Christie spent 71 days campaigning in the Granite State, and he had his best debate here just days before the primary - flustering rival Senator Marco Rubio into robotic repetition by criticising his lack of experience in office.

After all that, Christie garnered only 7 per cent of the vote.

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"While running for president I tried to reinforce what I have always believed - that speaking your mind matters, that experience matters, that competence matters and that it will always matter in leading our nation," Christie wrote in a Facebook post announcing his withdrawal.

He added: "I leave the race without an ounce of regret. I'm so proud of the campaign we ran, the people that ran it with me and all those who gave us their support and confidence along the way."

Christie's short-lived run for the presidency was a remarkable turnabout for a corruption-busting federal prosecutor who was elected Governor in 2009. He quickly made a name by battling the state's public-sector unions and engaging in well-publicised shouting matches at public meetings that became YouTube sensations.

Christie's career had once seemed so promising that in 2012 - after just two years in office - some Republicans urged him to challenge Mitt Romney for the GOP nomination. Christie demurred, saying he wasn't ready.

This time, he said he was. Christie was reelected by a wide margin in 2013 in New Jersey, a state where Democrats heavily outnumber Republicans. Then, as Republicans looked ahead to the 2016 election, Christie was an early front-runner in both national and New Hampshire polls.

But then came "Bridgegate." In the fall of 2013, two lanes leading to the George Washington Bridge - between Fort Lee, New Jersey, and New York City - were closed on the first day of school. The result was an enormous traffic jam, for four days running. The state first blamed the jam on a "traffic study." But later, evidence seemed to indicate that Christie's aides had arranged the jam on purpose, to punish Fort Lee's Democratic mayor for his refusal to endorse Christie's reelection.

One of Christie's former aides has pleaded guilty to conspiracy in that case, and two others have been indicted. Christie was exonerated by an independent, taxpayer-funded investigation, carried out by a law firm. But fundraising data has raised questions about that firm's independence: The news outlet NJ Advance Media reported that the firm's lawyers had given heavily to Christie's presidential bid.

Christie had expected that his in-your-face personality would be an advantage in this race: His slogan was "Telling It Like It Is." But the bridge scandal turned that plus into a minus, since it appeared that Christie's administration had used the power of the state to punish someone over a petty grievance.

As the 2016 campaign began, this was not Christie's only problem.

Conservative activists never warmed to Christie, believing he was too liberal on guns and social issues. They remained angry at him for a moment in the aftermath of Hurricane Sandy when Christie welcomed President Barack Obama to New Jersey. Christie's warmth for Obama, and his praise of the federal reaction, was good state politics but bad national politics - it was seen as having boosted the President in the last days of his contest against Romney.

Christie found himself constantly repeating that he hadn't actually hugged Obama, as many conservatives believed.

"When he got off Air Force One, I did shake his hand, which, I'll tell you what, civilised human beings do with other civilized human beings," Christie said in New Hampshire, according to a report in Time magazine.

Then Donald Trump got into the race, stealing the role that Christie had envisioned for himself: the brash loudmouth who got things done.

Christie wound up squeezed: He was too aggressive for voters who wanted a milder statesman and not aggressive enough for those who wanted Trump.

Still, Christie spent weeks in New Hampshire, trying to recapture his magic. In his town-hall meetings, his persona was heavily flavoured by his time as a prosecutor - Christie repeatedly imagined himself "prosecuting the case against Hillary Clinton," treating the Democrat like a defendant instead of an opponent.

But he also could play the part of regular suburban dad. In campaign appearances, Christie told audiences about how expensive his children's college tuition had become and bemoaned the unnecessary perks he had to pay for.

"There's an epidemic of rock-climbing walls!" Christie said at one appearance, joking that this epidemic had even reached New Hampshire, where they weren't needed.

"You've got rocks, man! You've got rocks everywhere!" Christie said. "You're the Granite State. Your state is named after rocks!"

At the final GOP debate in New Hampshire last weekend, Christie made one last plea to Granite State voters. "I've spent the last 13 years of my life focused on one thing: serving the people who have given me the opportunity to serve them. Not about politics, not about partisanship, but putting the people of my state and our country first.

"New Hampshire," he continued, "I spent 70 days here with you. You've gotten to know my heart. My heart is to help you solve the problems of your state and the problems of our nation. If you give me your vote ... I will do just that." Instead of propelling his presidential campaign, the Granite State ended it.

The end of Christie's campaign came right after its most prominent moment. At a debate just two days earlier, Christie accused Rubio of being a shallow candidate who could do little more than repeat talking points. And then Christie watched, with some delight, as Rubio repeated the same line three times in a row.

There would be no repeat of that performance. Even if Christie were to stay in the race, he probably would not have qualified for the next Republican debate.