Wisconsin Gov. Scott Walker (R) announced Monday that he was suspending his campaign for the White House, urging other candidates to follow suit. (Reuters)

Republican presidential candidates moved aggressively Monday to court the donor base of Wisconsin Gov. Scott Walker, whose abrupt exit from the race left his large national network of financial backers suddenly up for grabs.

Walker had attracted enthusiastic support from many wealthy contributors who were drawn initially to his campaigns against organized labor in Wisconsin and then saw him as a presidential candidate with the ability to mix conservative bona fides with executive experience.

Aides to former Florida governor Jeb Bush had started approaching top Walker bundlers after Walker failed to break out in last week’s GOP debate, urging them to jump ship, according to people familiar with the outreach.

Then, minutes after the news broke Monday afternoon that Walker was suspending his campaign, his fundraisers were inundated with calls — some from the candidates themselves.

The turn of events left many Walker donors reeling, with no clear direction where to shift their support.

Wisconsin Gov. Scott Walker announced at a news conference in Madison, Wis., on Monday that he is suspending his presidential bid. (Andy Manis/Getty Images)

“My heart is broken,” said New York investment broker Eric Anton, who is now considering Sen. Marco Rubio (Fla.), Sen. Ted Cruz (Tex.) and businesswoman Carly Fiorina.

“It’s a matter of who can win,” Anton said.

For many, it was too soon to consider shifting allegiances.

“I’m disappointed, first and foremost,” said Dallas-based biotech investor Chart Westcott, who gave $200,000 in June to Unintimidated PAC, a super PAC supporting the governor. “He was my first and best choice. I thought he had a very strong moral compass. Everything about the guy I admired and respect. He had a lot of backbone.”

Westcott said he and his family now plan to talk to a number of candidates and mull their choices. One thing he’s sure of: He is looking for someone who will “completely shake up the status quo in Washington, D.C.”

Marc Goldman, a Boca Raton, Fla.-based investor who donated $25,000 to the pro-Walker super PAC, said he was still contemplating what his withdrawal from the race means for the country.

“He has proven his willingness to take on the major challenges such as the ones that this country is facing and stand up to inordinate pressure,” he said. “That’s why I’m disappointed.”

Goldman said other campaigns had already reached out to him, but he needed some time to “get clarity for myself.”

“We are blessed with some wonderful choices, and they each deserve serious consideration,” he said.

Walker had a 50-state donor network that was far more extensive than might be expected of a Midwestern governor and former Milwaukee County executive. His hard-fought, costly campaigns against labor drew the support of conservative donors in the Koch political network, where he was a favorite. And his three wins at the polls in four years earned him credibility among the more establishment backers of the Republican Governors Association.

Deep-pocketed contributors helped Unintimidated PAC raise $20 million in less than two months this spring. Among the largest donors were Wisconsin billionaire Diane Hendricks, who gave $5 million; TD Ameritrade founder Joe Ricketts and his wife Marlene, who gave another $5 million; and Wisconsin shipping supply executive Richard Uihlein and his wife Elizabeth Uihlein, who put in $2.5 million.

Other major contributors included hedge fund billionaire John Paulson, Texas businessman Bob Rowling and investment banker Warren Stephens.

The super PAC was on track to raise an additional $15 million to $20 million by the end of the year, according to a Republican with intimate knowledge of the operation. Given that Walker is now suspending his campaign, the PAC plans to wind down its activities and return any remaining money to supporters, a spokesman said Monday night.

It is unclear how much money that will be, given that the super PAC now has to back out of television advertising buys, end contracts with vendors, pay final bills and shut down a months-long strategy. Once everything is wrapped up, the money will be sent back to donors, prorated to cover what the campaign had spent.

Already, there is an early effort underway to keep Walker’s finance staff together so they could help another candidate tap into his donor base. But what campaign the Walker team might join remains an open question.

Even before Walker stepped in front of the cameras Monday and made the news official, some of his biggest bundlers called one another with the same question: “Where should I go?”

There was no clear consensus, according to people familiar with the conversations, but among the favorites were Rubio, Fiorina, Ohio Gov. John Kasich and New Jersey Gov. Chris Christie. Bush is seen as having less appeal, in part because many of Walker’s backers view him as insufficiently conservative.

John Horne, an Arkansas-based GOP fundraiser who has been supportive of the Wisconsin governor, said that his departure from the race would benefit Rubio and Kasich the most.

“They are articulate and fit in well with both the establishment and the more conservative portions of the party,” he said. “In today’s social media world, you need a candidate who can communicate a message and connect with voters.”

Fred Malek, a longtime party fundraiser who serves as the RGA’s finance chairman, said he thinks many donors want to see a governor get the nomination.

“I think there will be a fair amount of Walker supporters gravitating to Kasich and Christie,” he said. “It really opens up the doors for them.”

Some donors are choosing to remain engaged with the campaign, but without picking a favorite.

Minnesota media executive Stanley S. Hubbard, an early Walker backer, made donations to Rubio, Fiorina, Christie and retired neurosurgeon Ben Carson after last week’s debate. Now, he plans to support all of them in the hopes that one will claim the nomination.

“I’m going to stick with those four,” he said.

Jenna Johnson contributed to this report.