WASHINGTON — Mitt Romney, who only days ago signaled he would explore running for president after repeatedly insisting he would not, is making a strong push that includes reaching out to fundraisers in Florida this week.

But the 2012 Republican nominee is running into a problem named Jeb Bush.

Bush is now weeks into his own aggressive foray into the presidential race and commands the loyalty of Florida's top fundraisers, many of whom were on board with Romney's last campaign.

That Romney would even make phone calls in Bush turf is a signal that he's serious and sets up a clash between two of the most well-known figures in Republican politics.

Bush's team expressed surprise at Romney's reversal ("Oh, no, no, no. No, no, no, no, no. No, no, no," he told the New York Times a year ago) but emphasized their game plan will not change and pointed to robust fundraising already under way.

"He was absolutely adamant before," said Mel Sembler, a St. Petersburg developer who was a national finance co-chairman for Romney in 2012. "I've heard him personally. He was very specific about it. He was not running. Apparently now he's decided he wants to mix it up a little bit."

"I have great affection for Mitt Romney and his wife," Sembler added. "They ran two very strong campaigns and I supported both of them. We wish him good luck, but I'm supporting my friend of many years, Jeb Bush."

Sembler is organizing a Tampa-area fundraiser this month and said "there's tremendous enthusiasm from people wanting to participate." He conceded Romney would change the dynamic. "It would make it more competitive, but Jeb is off and running and doing very well."

On Monday night in Orlando, attorney David Brown hosted a fundraiser for a super PAC backing Bush and said it "tremendously exceeded expectations." Brown would not reveal dollar amounts, per Bush team policy. "This was an easy ask."

A show of confidence is expected as both camps size each other up.

Romney enjoys broad name recognition — a new poll in Iowa released Tuesday showed him atop the hypothetical field, with Bush in second — and could tap into a national network of donors and supporters. He might also play on public dissatisfaction with President Barack Obama, a sort of buyer's remorse.

But he would be denied a major cash source in a critical swing state as well as on-the-ground support. Romney lost Florida and its 29 electoral votes to Obama in 2012.

In addition to Bush, Florida Sen. Marco Rubio is looking to jump into the race and is scooping up national media attention this week with the release of his new book.

Bush caught the field by surprise by announcing in December that he was actively exploring a run. He stepped up the pace this month with the formal rollout of a political action committee that will allow him to finance a staff and travel.

There's also the Right to Rise super PAC, which can take unlimited amounts of money. It's being led by a man who steered a super PAC for Romney in 2012, illustrating ties between the men.

The former Florida governor has been busily traveling the country meeting with donors and is in California this week for fundraising. Meanwhile, Romney was announced Tuesday as a last-minute addition to the Republican National Committee's winter meeting this week in San Diego. He will give brief remarks on Friday.

Romney had been saying for a long time that he wasn't going to run again, having mounted campaigns in 2008 and 2012. But chatter among his backers has grown in recent months and last week in Manhattan, Romney told some of his biggest past donors that he was looking at the race and wanted it to be known.

The Wall Street Journal reported that Romney "pointed to some reasons for another run, citing unrest overseas and concerns about the long-term health of the economy."

Some remain skeptical he will follow through but his phone calls this week show a seriousness.

Romney has challenges beyond competing with Bush and others for top donors. He came across in 2012 as insensitive to a broad section of the electorate struggling economically. During a fundraiser in Boca Raton in May 2012 he uttered now infamous remarks about the "47 percent" of people who do not pay income tax and how the "taker" class would never vote for him.

Rubio made an implicit criticism of that in his new book, American Dreams, recounting the story of a Florida mother of two who has to rely on government assistance to get by. "She is not a victim, nor is she a 'taker,' " Rubio wrote.

Romney's allies have been telling donors, and reporters, that he'll focus more on concerns of everyday people. They also say he'll run to the right of Bush, who has been portrayed as more of a moderate despite a decidedly conservative record as governor.

"Gov. Bush has great respect for Mitt Romney, but Gov. Romney's decision to move forward will not impact his decision or timetable for making one," spokeswoman Kristy Campbell said. "In the coming months, Gov. Bush will travel the nation to discuss his vision for the future of the country and in support of conservative candidates and conservative causes."