Mitt Romney got exactly the boost he needed Wednesday in the form of an endorsement by former Florida governor Jeb Bush, a move that came as GOP leaders and rank-and-file Republicans appeared to be coalescing around his presidential candidacy the day after a decisive primary victory in Illinois.

But amid the celebration, the Romney campaign faced a sudden distraction that underscored his lingering challenge in attracting conservatives to his cause.

A senior campaign aide suggested Wednesday that Romney might run a completely different campaign should he win the nomination. Asked in an interview on CNN whether Romney’s rivals might force him to tack too far right during the primaries, top adviser Eric Fehrnstrom said the general election will allow Romney to reintroduce himself to the voting public — and compared the campaign to an Etch a Sketch, a toy that can erase images with a simple shake.

The comment became a campaign sideshow on what was otherwise a pretty good day for Romney. Bush, one of the most influential voices in the party, announced that he will back the former Massachusetts governor, a surprising development after he sat out the Florida primary at the end of January.

“Primary elections have been held in 34 states, and now is the time for Republicans to unite behind Governor Romney and take our message of fiscal conservatism and job creation to all voters this fall,” Bush said. His father, former president George H.W. Bush, had already endorsed Romney.

Major Republican donors who had supported other candidates are defecting to the Romney camp, according to campaign finance paperwork filed this week. Among them is Texas home builder Bob Perry, who previously backed Texas Gov. Rick Perry (to whom he is not related) but last month wrote a $3 million check to a super PAC that supports Romney’s bid.

And FreedomWorks, a tea party organization led by former congressman Richard K. Armey (Tex.), appears to be softening its opposition to Romney’s presidential bid. The group’s vice president, Russ Walker, told the Washington Times that “the numbers favor Mitt Romney.” FreedomWorks will no longer oppose Romney’s candidacy, he said.

The developments gave credence to what Romney’s advisers have been saying for weeks: that he is the all-but-inevitable Republican nominee.

“It just shows a breaking of momentum toward Mitt Romney,” said GOP strategist Steve Schmidt. “He has been at this stage several times in the campaign, where he’s been at the precipice of becoming the de facto nominee. Each time he’s inched up to that line, he’s been knocked back. This is the first time that momentum seems to be pulling him over that line.”

Romney has won half the Republican National Convention delegates he needs to secure the nomination.

The announcements by Bush and FreedomWorks are significant because they represent divergent strands of the Republican Party and because both had expressed hesitancy to back Romney.

Senior Republicans were divided in trying to explain why Bush waited until now to endorse. “He’s lost any hope that we’ll have anyone better,” one operative said. Another Republican strategist who occasionally talks to Bush said the former governor “wanted to see someone earn it.”

Although conservatives across the spectrum appear to be taking heed, Romney still faces a challenge in winning over social conservatives, many of whom have flocked to rival Rick Santorum. And some of those who have shifted toward Romney lately say it is without much enthusiasm.

“We absolutely have not endorsed Mitt Romney for president. We don’t believe Romney has a consistent record of fiscal conservative policy,” said Jackie Bodnar, a spokeswoman for FreedomWorks. However, she said, “we absolutely are looking for the best conservative alternative to Barack Obama.”

On Wednesday, the Fehrnstrom quip allowed some Romney critics to renew their argument that he is an unreliable conservative.

“I think you hit a reset button for the fall campaign,” Ferhrnstrom said. “Everything changes. It’s almost like an Etch a Sketch. You can kind of shake it up and restart all over again.”

His opponents pounced, saying Fehrnstrom was conceding that Romney shifts his views with the political winds — a reputation that has dogged Romney since he entered the campaign. “Etch a Sketch is a great toy but a losing strategy,” Newt Gingrich said via Twitter. Santorum’s campaign passed out miniature Etch a Sketches on the campaign trail. The Democratic National Committee’s rapid-response team issued at least 13 statements on the matter.

After a campaign stop Wednesday in Maryland, Romney aides said the candidate would conduct a brief question-and-answer period with reporters. He took one query about the Etch a Sketch comment and then ended the event.

“The issues I’m running on will be exactly the same,” Romney said. “I’m running as a conservative Republican. I was a conservative Republican governor. I will be running as a conservative Republican nominee. . . . The policies and positions are the same.”

Richard Land, the political leader of the Southern Baptist Convention, said that one of the best things Romney has going for him is the Democrat he would face if he won the nomination.

“Do not underestimate President Obama’s unique ability to rally people around his opponent,” Land said, adding that he expects that social conservatives will begin backing Romney, who “increasingly looks like the nominee.”

A growing number of longtime GOP fundraisers are showing signs of uniting around Romney’s candidacy, giving millions to Restore Our Future, a super PAC that has played a pivotal role in running attack ads in key primary states.

Bob Perry, who is known for his support of the Swift Boat Veterans for Truth attacks in 2004, wrote a $3 million check to Restore Our Future last month, accounting for nearly half of the group’s February contributions.

Other major GOP figures who have put money into the pro-Romney super PAC in recent weeks include Texas billionaire Harold C. Simmons, another Swift Boat funder and a former bundler for George W. Bush and the 2008 nominee, Sen. John McCain (Ariz.); former Univision chief executive Jerry Pe­renchio; and Griff Harsh, husband of Hew­lett-Packard chief executive Meg Whitman, who is leading Romney’s fundraising efforts in California.

After Romney’s strong showing in Illinois, several people in the audience at his event in Baltimore County said they hoped they were watching a new phase of the campaign.

“I’m hoping that was the tipping point, I’m really hoping it was,” said Leanne Music, 65, a Republican from Arbutus. “I’m tired of hearing them talk about each other. I want to hear them talk about the real issues,” she said, noting how Romney said he thought he was “almost there” after Tuesday’s win.

“I think he’s starting to believe that it’s happening.”

Staff writers Aaron Davis in Baltimore and Chris Cillizza in Washington contributed to this report.