The rapidly shifting landscape in the GOP presidential race has set off a scramble for big donors among Mitt Romney and other established candidates, each of them rushing to secure high-dollar commitments in an attempt to fend off emerging rivals, according to senior campaign officials and fundraisers.

The moves follow the departure of Indiana Gov. Mitch Daniels and other potential contenders with strong ties to GOP powerbrokers, who are now casting about for new candidates to support. Operatives for Romney, the presumptive front-runner, and declared candidate Tim Pawlenty have been busy contacting major Daniels supporters and other uncommitted donors in recent days in hopes of securing crucial financial commitments for the months ahead, according to sources close to the talks.

A third possible candidate with strong establishment credentials, former Utah governor and China ambassador Jon Huntsman Jr., kicked off a fundraising trip through California last week in hopes of drumming up support for his own presidential bid. Huntsman also met in Maine with former president George H.W. Bush, who has granted audiences with several top candidates seeking help from the Bush family and its far-flung network of supporters.

The developments signal a new phase in the unsettled GOP presidential contest, after recent announcements by Daniels, former Arkansas governor Mike Huckabee and Mississippi Gov. Haley Barbour that they would not seek the nomination. At the same time, a trio of insurgents — former senator Rick Santorum (Penn.), Rep. Michele Bachmann (Minn.) and former Alaska governor Sarah Palin — are jumping into the race or, in Palin’s case, sending fresh signals of a possible run.

The push for donors by Romney and Pawlenty is aimed in part at discouraging these emerging hopefuls, who have shown the ability to raise money in the past but whose financial prospects in the 2012 race are less clear. The candidates also are seeking to demonstrate their ability to take on President Obama, whose campaign is poised to meet or exceed the $750 million he raised in 2008.

The May 22 departure of Daniels, in particular, has set off a frenzy to line up support among the Indiana governor’s influential circle of friends, many of whom know him from his time as budget director in the George W. Bush administration. Dozens of “Pioneers,” “Rangers” and other prominent Bush bundlers have remained uncommitted for 2012.

The Daniels effect

Romney backers say Daniels’s decision is especially beneficial to Romney, a former Massachusetts governor and equity fund manager who shares close ties to many of the same corporate executives and Wall Street investors who would have been attracted to Daniels. Romney in recent years has raised nearly half of his money from the financial sector.

“We very much expect a number of Daniels’s supporters to come Romney’s way,” said Emil Henry Jr., a Bush-era Treasury Department official who is helping lead Romney’s fundraising efforts.

This early fundraising period also poses a crucial test for Pawlenty, a former Minnesota governor who so far has struggled to gather the financial resources needed to face Romney in a long primary fight. In a major fundraiser in Minneapolis last month, Pawlenty took in about $800,000; Romney, by contrast, raised $10.25 million in a single day during a telethon fundraiser in Las Vegas.

Greg Slayton, a former Bush fundraiser and Bermuda ambassador who supports Pawlenty, said the Daniels decision “is a turning point” for Pawlenty, who formally announced his candidacy May 23 and is poised to attract donors unhappy with Romney’s prospects.

“You’ve got 50 percent of Republican donors, maybe 40 percent, who a month ago were saying, ‘Just hold on, I’m waiting to see if Haley runs or Huckabee runs or Daniels runs,’ ” said Slayton, a former venture capitalist who teaches at New Hampshire’s Tuck School of Business at Dartmouth. “But now those guys aren’t running. The race now is very clear.”

Rick Hohlt, a Washington lobbyist and veteran GOP fundraiser, is one Daniels supporter who is getting a lot of sudden attention. The day after Daniels’s departure, Hohlt said, he got phone calls from Vin Weber, the former congressman who is now a Pawlenty adviser, and Spencer Zwick, Romney’s national finance chairman.

It wasn’t the first time that he’d heard from them. Zwick even invited Hohlt to New Hampshire to spend a day with Romney about two years ago.

“The Romney operation has been very, very, very aggressive and very sophisticated for a long time,” Hohlt said. “Where Pawlenty is out there trying to build it, Romney’s already built it.”

Hohlt said he hasn’t made up his mind on whom to support, partly because he hasn’t gotten to know Pawlenty. “You’re obviously making an investment in that person as far as their success, so you have to make some judgment about who would go the distance,” Hohlt said. “At the same time, you want to have someone who believes in some of the same policies.”

Changing lineup

The fundraising surge comes amid a rapidly shifting cast of characters in the race: Santorum and Romney plan to formally enter the race in coming days, while Bachmann will clarify her plans. Meanwhile, Palin, whose chances had seemed to fade in recent months, has suddenly reignited speculation with the release of a promotional movie about her Alaska political career and the launch of a bus tour that began in Washington on Sunday.

As for fundraising, the precise outlines of the GOP money contest remain unclear; the first major disclosure reports aren’t due until July.

But so many major GOP donors still sitting on the sidelines underscores the uncertainty surrounding this year’s Republican field. Many party insiders have made little secret of their unhappiness with the current crop of candidates, including Romney and Pawlenty, while much of the public debate has been dominated by the temporary Donald Trump candidacy, Newt Gingrich’s jewelry purchases and other sideshows.

“A lot of us are disappointed that it’s not a Haley or a Mitch,” said one Republican fundraiser from California, who spoke on the condition of anonymity in order to talk freely. “We don’t need a flashy candidate to beat Obama. We need someone who is plain, simple-talking, and maybe that’s Pawlenty.”

On the other hand, this fundraiser said, “the problem with Pawlenty is that people don’t know who he is.”