Governor of Mississippi Won’t Run for President

In a telephone call to supporters, followed by a brief statement, Mr. Barbour said he lacked the “absolute fire in the belly,” that a candidacy would require. He apologized for flirting with a presidential bid over the last six months and then backing away, but said he had concluded that he was not ready to dedicate himself to the “all-consuming effort” a campaign would require.

“I cannot offer that with certainty,” he said, “and total certainty is required.”

The decision by Mr. Barbour, 63, provided the biggest shake-up yet of the 2012 presidential race. His departure adds another layer of uncertainty to the wide-open fight for the party’s nomination and set off a scramble among other candidates seeking to sign up his donors and supporters.

Throughout the spring, Mr. Barbour has been traveling to Iowa, New Hampshire and South Carolina, testing his support among Republicans who cast the first votes. He recruited a team of operatives in those states, along with national campaign strategists, and rivals expected him to join the first Republican debate next week in South Carolina.

But his candidacy faced many challenges. As a lobbyist, for example, he represented tobacco companies, the pharmaceutical industry and several foreign governments. He sought to sell the experience as an advantage, telling audiences, “I saw the sausage factory up close,” but his aides braced for intense scrutiny.

Mr. Barbour founded the Washington lobbying firm now known as BGR in 1991 with Ed Rogers, a close friend who had worked with him in the Reagan White House. The next year, Lanny Griffith, who worked in the administration of President George Bush and also hailed from Mississippi, joined them. They formed the foundation of a powerhouse firm with close ties to the Republican establishment.

Mr. Barbour left the firm in 2004 when he became governor of Mississippi, but associates say he is a frequent visitor to the office when he is in Washington. Since his formal departure, reports have shown that he has continued to draw hundreds of thousands of dollars from a blind trust that held stock in the firm’s parent company.

His decision touched off a new round of speculation about Gov. Mitch Daniels of Indiana, a close friend who is also weighing the possibility of entering the Republican race. Mr. Daniels has said he intends to make a decision as early as next month. (Representative Ron Paul of Texas is set to announce on Tuesday that he is opening a presidential exploratory committee.)

It remained an open question where Mr. Barbour’s supporters would go — or if he would try to direct them to one candidate — but his decision could help other contenders, including those trying to emerge as the leading alternative to Mitt Romney, a former governor of Massachusetts. Tim Pawlenty, a former Minnesota governor, probably faces an easier time winning establishment support with Mr. Barbour out of the picture.

Newt Gingrich, a former speaker of the House from Georgia, is now expected to be the only Southerner in the race. That could help him in the South Carolina primary, which follows the opening contests in Iowa and New Hampshire.

Katon Dawson, a former chairman of the South Carolina Republican Party, said in an interview that he believed Mr. Gingrich would stand to gain the most from Mr. Barbour’s decision. But Mr. Dawson said that the contest remained remarkably unpredictable and that other potential candidates, like former Gov. Mike Huckabee of Arkansas, needed to make their decisions soon.

There had been questions about Mr. Barbour’s health. He had back surgery last week, hoping to correct a condition that caused him noticeable pain. Last month, he said he had lost 20 pounds and intended to lose 20 more by the end of April.

But nine days ago, after speaking at a Republican county convention in South Carolina, Mr. Barbour grabbed a doughnut before heading for the door. He had not been seen doing that — in public, at least — in months.

Eric Lichtblau contributed reporting.