Jeb Bush’s announcement Tuesday that he is actively exploring a 2016 presidential run scrambles the large Republican field, thrusting him to the front of the pack and locking up a huge swath of longtime party fundraisers being wooed by other candidates.

Bush, the 61-year-old son of one president and the brother of another, declared in a Facebook post Tuesday that he intends to set up a leadership PAC in January to “discuss the most critical challenges facing our exceptional nation.”

His potential candidacy raises the prospect that the upcoming White House race will be a dynastic match between Bush and former Secretary of State Hillary Rodham Clinton, who is the heavy favorite for the Democratic nomination if she chooses to run.

But first, Bush would have to get through the GOP primaries, where his conservative credentials are likely to be challenged by activists on the right who scorn his support for immigration and education reform.

For now, the early move by the former Florida governor is expected to severely undercut the financial backing for other possible 2016 contenders — especially New Jersey Gov. Chris Christie, Texas Gov. Rick Perry and Sen. Marco Rubio (Fla.). In addition, a Bush candidacy could make it difficult for lesser-known potential candidates, such as Ohio Gov. John Kasich and Indiana Gov. Mike Pence, to gain traction, well-connected Republicans said.

Bush’s declared interest also punctures the rationale for a candidacy by Mitt Romney, the 2012 GOP nominee who occupies a similar space within the party establishment.

A Washington Post-ABC News poll released Tuesday found Bush with a narrow edge over a crowded field of potential GOP contenders if Romney were not in the race. Bush garners 15 percent support among Republicans and GOP-leaning independents, with Sen. Rand Paul (Ky.) and Rep. Paul Ryan (Wis.) each netting 11 percent. Support for all three top candidates is within the poll’s five-point margin of sampling error.

If Romney ran again, he would enter the race with 20 percent support, leading his rivals by 10 points or more.

The survey found that the GOP field is the most fractured it has been in more than two decades. Without Romney in the race, support is split among more than a dozen contenders, with no candidate having a clear base of support.

Bush’s early announcement could force others contemplating a bid — particularly Romney and Christie — to speed up their timetables.

“This frontloads everything,” said Bobbie Kilberg, a top Republican fundraiser in Virginia. She added, “What he’s saying is, ‘I’m out and I’m ready,’ and so it puts pressure on others in the center-right to do the same.”

The most immediate impact of the decision is on the money race, which has remained largely static as party donors waited to see what Bush would do. Locking up financial backers is an urgent task for would-be candidates, who will likely need to raise at least $100 million to get through the primaries.

Former Florida governor Jeb Bush told fall 2014 graduates, "No matter what path you choose, don't let anyone else ever tell you how big to dream." (University of South Carolina)

Already, large numbers of center-right financiers have begun rushing to Bush, draining the pool of financial backers available for other candidates. Advisers close to Bush said that they fielded phone calls all day from contributors eager to support him if he runs.

“I think Jeb’s decision this early unexpectedly freezes many potential donors and bundlers who were exploring going with Christie or another candidate,” said John Horne, a top party fundraiser in Arkansas.

By midday Tuesday, Kilberg said she had received calls from a dozen donors asking, “Okay, what do we do now?”

One major advantage for Bush is the vast network of former ambassadors and onetime senior government appointees who served in the administrations of his father and brother.

Mel Sembler — ambassador to Australia for President George H.W. Bush and the ambassador to Italy for President George W. Bush — said Tuesday that he is committed to raising money for Jeb Bush, even though he has been an admirer of Rubio.

“I think that this is going to help Rubio make a decision, and it would be pretty difficult for him to compete against Jeb,” Sembler said. “I have great affection for Marco, but Jeb has the executive experience, and there’s a difference. That’s the problem we’re having right now: Our present president came to office without executive experience, and I’m afraid it’s showing.”

But other donors asserted that Christie, Rubio and other potential Bush rivals are substantive, serious leaders who still could attract their own financial support.

“It’s not a monopoly situation,” said one prominent GOP fundraiser, who requested anonymity to speak candidly. “Jeb Bush is certainly going to have a formidable fundraising machine, but there’s plenty of room out there for Rubio and for others to raise money.”

Speaking to reporters at the U.S. Capitol on Tuesday, Rubio said, “I’ve got a lot of respect for Gov. Bush and I think he’d be a formidable candidate if he decides to run. But from my perspective, my decision is going to be based on where I can best advance my agenda for restoring the American dream.”

A Perry representative sounded a similar message. “This is not going to impact what Rick Perry decides to do,” said Jeff Miller, the Texas governor’s political strategist. “Rick Perry will still raise a significant amount of money to be competitive if he decides to run for president.”

Wisconsin Gov. Scott Walker said Bush’s moves would not impact his plans.

“Whatever decision I make will be based on me, my family and my state and what I may or may not be able to do for the country, and not based on anybody else who may or may not be in the race,” Walker told reporters, according to the Milwaukee Journal-Sentinel.

Advisers to Christie were notably silent and did not respond to requests for comment on how Bush’s entry in the race would impact the New Jersey governor.

Amid the frenzy of chatter set off by Bush’s announcement, there were early signs of the backlash he would face among some on the right.

“I don’t think we need another Bush. Period,” Sen. Tom Coburn (R-Okla.) told reporters. “I like ’em all, but I don’t think we need another Bush.”

L. Brent Bozell III, chairman of the group ForAmerica, said that while he has “great admiration for the Bush family,” he and other conservatives reacted with groans at the thought of him running.

“It’s not just the Bush name, it’s the Bush agenda,” Bozell said, noting that the former governor is a proponent of the Common Core education standards and immigration reform. “Those are really going to get the base jumping.”

Plus, he added, “I just can’t think of anything more boring” than a Clinton-Bush matchup.

Democrats rushed to raise money off Bush’s news and top party officials scoffed publicly at the prospect of his candidacy. But privately, strategists close to Clinton have long viewed the former Florida governor as the biggest threat to her bid because of his potential to win over swing voters and Latinos.

John Ellis Bush, who goes by the nickname “Jeb,” studied Latin American issues in the United States and abroad, became fluent in Spanish and met his wife, Columba, in Mexico. They settled in Florida, where Bush immersed himself in real estate and other business interests, GOP politics and Hispanic culture.

In 1994, Bush lost his first run for governor to Democrat Lawton Chiles, but came back to win in 1998 with a large share of Hispanic and white moderate voters. During eight years as governor, Bush earned a reputation as a conservative and a policy wonk, championing a private school voucher program, overhauling Medicaid and slashing taxes. He is staunchly pro-life, drawing national attention for his efforts to keep a brain-damaged woman, Terry Schiavo, on feeding tubes over the objections of her husband.

Since leaving office in 2007, Bush has become a GOP thought leader, especially on education and immigration issues through several nonprofit foundations. He also has a host of finance and private equity interests that would draw scrutiny in a campaign, including advising Lehman Brothers and Barclays.

Bush could still decide not to enter the race. Kristy Campbell, a spokeswoman for Bush, said “he has not made a final decision on pursuing a candidacy.”

“This is a natural next step — to actively explore the possibility of a run and gauge if there would be support for one,” she added.

Setting up a leadership PAC allows Bush to raise money to pay staff, finance his travel and begin building an e-mail list of supporters without officially jumping in the race. Under federal rules, Bush cannot use the PAC to underwrite his campaign activities, but he can use funds to contribute to state and local officials in key primary states.

The structure also allows him to solicit money from the same donors twice: once for the leadership PAC, and then again for a presidential campaign.

This past weekend, Bush gave an extensive interview to a Miami television station in which he announced plans to release an e-book and all of his e-mails from his tenure as governor.

In the interview, he outlined the philosophical approach he would take in a campaign, saying, “You have to be true to who you are.”

“In the world we’re in now, where there’s such deep disaffection, where people don’t trust institutions, they don’t trust the political parties,” he said, adding that a candidate can’t “just kind say you’re for one thing, and then change it after you win the primary.”

The former governor indicated that he would not back away from his support for Common Core education standards or a comprehensive immigration overhaul.

Bush said he thinks Romney was hurt in the 2012 primaries when he “got sucked into other people’s agendas” and moved too far to the right. He also said he thinks “almost daily” about what would have happened if Romney had won the White House instead of President Obama.

“Winning with purpose, winning with meaning, winning with your integrity is what I’m trying to talk about,” Bush said.

Scott Clement, Ed O’Keefe and Sean Sullivan in Washington and Robert Costa in Des Moines contributed to this report.