Saying it was time to give the "next generation of Republican leaders" a chance to serve. 2012 Republican presidential nominee Mitt Romney told supporters in a conference call on Friday that he would not be a candidate for president in 2016.

On Thursday, Romney sent an email to donors and activists inviting them to a conference call where he planned to announce his intentions. Just prior to the call, several news outlets broke a story saying that Romney was going to run. They were forced to issue hasty retractions when Mitt made his plans known.

Associated Press:

Aides said it was a deeply personal and even painful decision for the 2012 Republican presidential nominee. He insisted he could win the next election if he ran, but his announcement followed a three-week fact-finding effort that revealed significant resistance to a third campaign.

"I believe that one of our next generation of Republican leaders, one who may not be as well-known as I am today, one who has not yet taken their message across the country, one who is just getting started, may well emerge as being better able to defeat the Democrat nominee," Romney told supporters on a conference call. "In fact, I expect and hope that to be the case."

The remark was both a recognition of his own limitations and an indirect swipe at the man who created the urgency behind Romney's brief flirtation with a third presidential campaign. That is former Florida Gov. Jeb Bush, the son and brother of former presidents, who is speeding toward a campaign of his own.

Bush and New Jersey Gov. Chris Christie would have served as Romney's most likely rivals for the support of the GOP establishment, and both men felt an immediate impact. The announcement sparked a rush of activity by Romney loyalists — operatives and donors alike — suddenly freed to support another White House hopeful as the crowded 2016 field begins to take shape.

Devoted Romney supporter Bill Kunkler, part of Chicago's wealthy Crown family, said he was disappointed by Friday's news but now was all-in for Bush.

"I'll work for Jeb. Period. And no one else," Kunkler said, noting that he planned to attend a Feb. 18 Chicago fundraiser for Bush hosted by former Romney backers.

A private poll taken by a wealthy donor purported to show Romney far ahead in the first 20 primary states. But that was yesterday. Romney as an announced candidate would have become a target for not only the right, but other establishment types like Jeb Bush and Chris Christie He also had been bleeding donors and potential staff to other candidates. A recent Iowa poll showed his negatives rising. It seems that Romney as a potential candidate was a lot more attractive than Romney as an in the flesh candidate.

This from Bloomberg's Mark Halperin fleshes out the Romney decision:

The second “no go” reason weighed far more heavily on Romney—and was likely the dispositive one. People close to the former governor say he believed he would beat Hillary Clinton in a general election matchup if the election were held today. But, like many election watchers, Romney anticipates a vicious Republican nomination fight that will damage and deplete the ultimate winner, while Clinton, virtually unchallenged for her party’s nomination, will be luxuriantly free to squirrel away hundreds of millions of election dollars and step into the general arena, rich and refreshed, against a shattered GOP nominee.

Obviously Jeb Bush benefits the most from Romney's decision. But it also affects Chris Christie. It makes a run by the New Jersey governor less likely. Splitting the establishment vote 3 ways would have meant that Bush, Romney, or Christie would not have been entirely out of the race much before the March slew of primaries. A two man establishment race now forces Christie to go big and go early with money and organization. And Jeb Bush is already miles ahead.

In fact, the Romney announcement has speeded up the timetable for other candidates. With Romney out of the picture, donors, activists, and political staffers will now quickly choose sides. Where many candidates might have been contemplating an early spring launch, the pace is going to pick up in the next 30 days and it is likely that several candidates will announce before or soon after March 1.

Romney was getting positive signals from the political pros who staff, finance, and run campaigns. But the silence of the base - or outright hostility - meant that he wouldn't have had much of a chance should he have decided to run.