New Jersey Governor Chris Christie has announced that he is not running for the White House, after weeks of calls for him to enter the race.Mr Christie held a news conference at the governor's office, where he told reporters: "Now is not my time."
The Republican has spent the past week reconsidering calls from the party to run for president.
He would not be drawn on endorsing any of the Republican pack, currently led by Mitt Romney and Rick Perry.
"In the end what I've always felt was the right decision remains the right decision today," he said.
"Now is not my time. I have a commitment to New Jersey that I simply will not abandon."
He added: "You're stuck with me".
'Too late' Encouragement from Republicans like Henry Kissinger, Nancy Reagan and Barbara Bush had led him to reconsider a bid.
But correspondents said that jumping into the race a few weeks before the filing deadline would have left Mr Christie far behind his rivals in fundraising and organising.
The Associated Press news agency reports that advisers to Mr Christie had said his decision was in part because it would have been too late to set up the needed infrastructure.
Although time has ticked away, leaving virtually no chance of another candidate coming in, Republicans still cast around for a saviour ”
Elected governor in 2009, Mr Christie has a reputation as a tough-talking, fiscally conservative governor.Mr Christie did not rule out a future presidential bid and used his moment in the national spotlight to criticise President Barack Obama.
"This is an example of someone who has failed the leadership test," Mr Christie said. "You can't be taught how to lead and make decisions."
His announcement will swing focus back to the two leaders of the race for the Republican nomination to challenge Mr Obama in the November 2012 presidential elections.
But Texas Governor Perry's lead has proved fragile after he was criticised for controversial remarks on the campaign trail and over his TV debating performance.
And former Massachusetts Governor Romney has struggled to win over Tea Party supporters and conservative Republicans.
Meanwhile, businessman Herman Cain's profile has risen after his strong debating performances.