Jeb Bush became the first big name to enter the 2016 presidential fray on Tuesday, shaking up a field that was waiting to see whether he’d enter the GOP race.

The former Florida governor’s announcement that he was “actively exploring” a bid sent a clear signal to donors, campaign staffers and his rivals of his seriousness about a White House run.

“Rarely has a candidate launched an exploratory committee and received findings that dissuade them from running,” said Ryan Williams, a former spokesman for Mitt Romney’s 2012 campaign. “You don’t go exploring and determine that things are great or that there are better candidates than you. It’s a move that leads to a run.”

Bush, who also said Tuesday that he would set up a leadership PAC, has been moving towards a White House bid for some time.

He’s lost weight and been a regular on the public speaking circuit. Over the weekend, he announced he’d release 250,000 emails from his time as governor, along with an e-book laying out his policy positions. 

Bush also met recently with 2008 Republican presidential nominee, Sen. John McCain (R-Ariz.), who on Tuesday said the two discussed the “ins-and-outs and mechanics of campaigning.”

“Not surprised, not surprised,” McCain said of Bush’s announcement.

While Bush’s candidacy appeared increasingly inevitable to GOP insiders, Bush’s timeline has been more aggressive than most of the other potential contenders, who are largely setting mid-2015 deadlines for themselves. 

“It’s a smart political move on his part given where he stands in the ecosystem of candidates as the preferred establishment candidate among donors,” said Florida Republican strategist Rick Wilson.

Bush’s move puts pressure on the more than a dozen potential GOP candidates who are mulling their own bids for the nomination. His entrance could tamp down the ambitions of some second-tier candidates who have been working donors and supporters behind the scenes waiting to see how the field shakes out. 

“Some of the dark horses could be scared away,” Williams said.

There might not be room now in the crowded field of potential contenders for another centrist along the lines of Gov. John Kasich (R-Ohio).

But for those who view themselves as the top tier of candidates, Bush’s move is more something to ponder rather than an inciting event. 

“Someone who has been laying the groundwork for this for the last two years won’t be dissuaded to run,” Williams predicted. “It’s not as though [New Jersey Gov. Chris] Christie, [Sen. Marco] Rubio, [Rep. Paul] Ryan, or [Gov. Scott] Walker and others have just been sitting on their hands. They’ve been campaigning and building their donor bases as well.” 

Williams noted that Rubio has “spent the last four years expanding his reach across the country and building relationships.” 

Indeed, the Florida senator was the first candidate to respond on how Bush’s candidacy would impact his own. Since the two share many of the same donors and Rubio’s star rose under Bush’s wing in Florida, there has been speculation a Bush candidacy would put an end to Rubio’s efforts, but the senator’s team quickly downplayed that idea.  

“Marco has a lot of respect for Gov. Bush, and believes he would be a formidable candidate,” Rubio spokesman Alex Conant said. “However, Marco’s decision on whether to run for president or reelection will be based on where he can best achieve his agenda to restore the American dream — not on who else might be running.”

Walker spoke with The Associated Press. Bush's action "doesn't affect me one way or another." My own decision will be “based upon me, my family and my state and what I may or may not be able to do for my country not based on anyone else who may or may not be in the race." 

Texas Gov. Rick Perry (R) echoed that sentiment, with one of his aides telling the Houston Chronicle that Bush's decision "won’t affect the governor’s decision-making process."

Romney and Sen. Rand Paul (R-Ky.), with their campaign infrastructures and wide donor bases, are also likely to be unmoved by Bush’s announcement. His move may not impact conservative firebrands like former Arkansas Gov. Mike Huckabee (R) and Dr. Ben Carson either, who will be chasing a different stripe of GOP voters in the primaries, should they run. 

Sen. Ted Cruz (R-Texas) wouldn’t respond directly to a question from The Hill about whether Bush’s candidacy would weigh on his own, but insinuated that it wouldn’t matter because the two would be dipping into different pools of GOP supporters.

“It’s going to be a choice for the primary voters,” Cruz said.

Bush’s early moves will buy him time to build out a strong campaign infrastructure by putting a freeze on the major donors and campaign staffers that will be casting their lots between the candidates soon enough.

“There’s going to be a lot of competitors out there who are going to get in the race soon,” said Charlie Black, a Republican strategist and adviser to McCain. “It’s good to get that committee running early to line up donors and start building out your staff.”

“Jeb is giving those donors time to take a breather and not answer the phone for other potential candidates for a while,” Wilson said. 

Bush’s challenge now will be to reach out to conservatives who vote in the early primary and caucus states.

Republican strategists crow about Bush’s conservative record from his time as governor, but he’s at odds with the conservative base on issues like immigration and education.

Bush didn’t do himself any favors when he said last month that a potentially strong general election candidate must be prepared to lose the nomination if it means compromising his principles by tacking too far to the right in the primaries.

The Democratic National Committee quickly circulated a fundraising email Tuesday to “think about how President Bush worked out last time.” But even some Democrats admit he would be a formidable opponent, even against Hillary Clinton, the front-runner on their side. 

“Jeb Bush would be the most difficult Republican to beat in the fall of 2016. He'd be the best Republican in terms of someone who could be president, and me saying that probably kills him. And he has virtually no chance of winning the nomination, because of immigration, and because of his stand on Common Core — he virtually authored it,” former Gov. Ed Rendell (D-Pa.), a Clinton ally, told The Hill. 

“You can’t discount a Bush. Not at all,” one Democratic consultant who worked on Clinton’s 2008 presidential campaign told The Hill earlier this month. “For a Republican, he makes one of the most salient points for Hispanics and their perspective and he could easily carry Florida, a swing state."

Some are exasperated by the idea that Bush has been painted as a moderate or centrist Republican. Sen. Bill Nelson (D-Fla.) called him “Tea Party-ish,” and said “his positions have not moved to the center, only his talk has moved to the center.”

Wilson said Bush needs to kick back hard against the idea that he’s not a true conservative.

“He should criticize corporatist cronies and D.C. squishes and blow them the hell up, and then he might have some more traction with conservatives and buy himself some more time,” Wilson said. “He governed as a remarkable conservative. Nobody in Florida or the nation ever thought Jeb was anything more than a full-throated, red-toothed … Republican.”

— Cameron Joseph contributed. 

This post was updated at 7:34 p.m.