Washington — Former Florida governor Jeb Bush said on Tuesday that he would “actively explore” a presidential run, immediately sending reverberations through the potential Republican field, tying up donors whom other candidates are courting and forcing contenders to accelerate their own considerations for 2016.

Bush became the first Republican to take an overt step toward a White House bid. He announced on Facebook that he would create a political action committee next month, allowing him to raise money and travel the country ahead of an eventual decision, and spent part of the day calling donors.

“In the coming months, I hope to visit with many of you and have a conversation about restoring the promise of America,” wrote Bush, a son and brother of presidents, indicating he had made his decision after talking with his family over Thanksgiving.

By announcing that he is considering a 2016 presidential bid and making official what has become increasingly apparent in recent weeks, Bush, 61, quickly reshaped a Republican race that had scarcely begun forming.

Bush’s early move amounted to a pre-emptive strike on his most likely rivals for the blessing of establishment-oriented contributors and party officials.

The most immediate effect of his announcement was with his party’s financial bundlers, those who raise the most money for candidates. Many of those donors have long ties to the family that has dominated Republican politics for the last quarter-century and were waiting for a signal that the younger brother of former President George W. Bush was serious about a campaign.

With that sign given, some of his loyalists moved to declare the chase for the most sought-after donors effectively over — a notion advisers to other potential candidates dismissed.

“If he runs, Jeb assumes the mantle of the centre-right, establishment candidate, which, along with his family network, means he will have an incredible finance operation,” said Brian D. Ballard, a Florida-based lobbyist and contributor.

Ballard, who stepped outside from a lunch with a group of Miami business leaders to talk with a reporter on Tuesday, said that among the executives at the lunch, there was a mix of excitement about a possible Bush run as well as hope that he would take the next step.

Such support-in-waiting illustrates the difficulty that Bush’s fellow Florida Republican, Sen. Marco Rubio, could have financing a campaign if many of his crucial home state backers support Bush.

Rubio, whose term is up in 2016, said through a spokesman that he believed Bush would be a formidable candidate but reiterated that his decision to run would not be based on “who else might be running.”

Bush’s move also may make fund-raising more difficult for Governor Chris Christie of New Jersey, whose base of New York-area donors will face pressure from Bush loyalists to hold out for a familiar political brand.

Further, the possibility of a third campaign by Mitt Romney, the Republicans’ 2012 standard-bearer, now seems less likely. Some party elites were eying a Romney revival in large part because they were seeking a candidate formidable enough to take on former Secretary of State Hillary Rodham Clinton.

Tension between supporters of the two Republicans has been rising, and at least one Romney adviser has expressed irritation to Bush’s backers about some of the former Florida governor’s recent criticism of Romney’s 2012 campaign.

Bush’s allies, for their part, have been asking donors to share what Romney’s loyalists have been saying about his own plans. Some contributors believe Bush is seeking to force Romney’s hand by stepping forward at this early date, raising pressure on donors with ties to both men to pick a side.

With bundlers, elected officials and party activists now given the chance to show their support early for Bush, and perhaps win a chit for a future appointment, other prospects will have to quickly indicate their plans.

“If you’re going to run, go do it,” said Robert T. Grand, an Indiana-based Republican donor, who was one of the leading donors to George W. Bush’s 2004 campaign. “I think you’ve got a short period of time. This announcement triggers the start.”

“Now that he has entered the ring you will see others doing so fairly rapidly because there will be a race for funders,” added Dirk Van Dongen, a Washington lobbyist and bundler who will back Bush.

Bush’s allies stressed that he had not made a final decision and purposefully created a leadership political action committee instead of an exploratory committee, which for legal purposes is the same as a campaign committee.

On advice from his new campaign lawyer, Washington attorney Charles R. Spies, the former governor set up an organisational vehicle that will let him employ staff and raise the legal maximum amount of money from donors for as long as he considers his decision. Bush could then return to those same contributors for additional money if he ultimately established a full-blown campaign committee.

The question that looms over yet another Bush candidacy, though, is whether he can appeal to rank-and-file Republican primary voters as much as he does the party’s elites. In that sense, Bush’s early lean toward a run is not entirely bad news. If it turns out that he cannot appeal to the party base or backs away from a run entirely, there would be time for others to make a move.

Conservative leaders said Bush needed to move swiftly to address questions about such issues as his support for Common Core — a set of standards for students from kindergarten through high school.

“It’s going to be an issue for him and he’s going to have to start having conversations with conservatives in the party, which I’ve not seen yet,” said Tony Perkins, president of the Family Research Council, a conservative policy and lobbying organisation.

For Democrats, though, Bush’s step toward a campaign was cause for concern, as many said the Spanish-speaking former governor of Florida, perhaps the most electorally pivotal state in the country, would be the toughest Republican to defeat.

“I keep reminding people Michael Corleone was the younger brother of Fredo,” said Democratic strategist Paul Begala, comparing characters from “The Godfather” to Bush family dynamics.