Correction: An earlier version of this story included a quote from Romney: "If I am president I will save Social Security and Medicare, and make sure they do not kill the future generations." The more complete version of that quote, which was inaudible to the audience because of loud applause at the event, was: "If I am president I will save Social Security and Medicare, and make sure they do not kill the future generations with excessive taxes." The story also incorrectly stated the the degree to which Romney would limit federal spending. It would be 20 percent of GDP, not 17 percent.

To listen to Mitt Romney these days is to wish at times that someone would give him back his PowerPoint.

Romney, after all, made a fortune on his ability to make a crisp presentation and close a deal. As a governor pushing for a landmark approach to health-care coverage in Massachusetts, the former management consultant won over doubters by putting together a slide presentation and taking it all over the state.

So why is he having so much trouble making the sale with the Republican electorate?

Many of his allies and supporters are increasingly worried that the problem is Romney himself.

Until now, Romney and his well-financed allies have been able to dispatch any opponent who presents a threat by drowning the potential usurper with negative advertising.

But the fact that a new one emerges each time he vanquishes another betrays the existence of a deeper discontent with Romney himself.

“To be elected president, you have to do more than tear down your opponents,” said Ohio Attorney General Mike DeWine, a former Romney supporter who on Friday defected to the camp of former Pennsylvania senator Rick Santorum, the latest to emerge as an alternative to Romney.

“You have to give the American people a reason to vote for you — a reason to hope — a reason to believe that under your leadership, America will be better,” DeWine added. “Rick Santorum has done that. Sadly, Governor Romney has not.”

As Romney has adjusted tactically to a primary battle that is turning out to be tougher than he bargained for, some of his backers now say they fear that Romney is reinforcing the doubts that voters already have about him.

Businessman Peter Thomas, for instance, showed up at a Romney appearance near Grand Rapids, Mich., on Wednesday, but admitted he is now leaning more toward Santorum.

“He’s more blue collar, his story,” Thomas said of Santorum. “He’s a straight shooter. He says what he means. He won’t drift in the wind.”

Repairing a candidate’s message can be as mystical an art as fixing a golfer’s swing. Especially in Romney’s case, where there are many diagnoses of what, precisely, is wrong.

“The worst thing is fake passion, where they take the same script and tell him to yell louder,” said Mike Murphy, who is Romney’s former political consultant and who remains in touch with the candidate.

One fundraiser, who did not want to be identified publicly criticizing a candidate in whom he invested, said Romney’s difficulty is connecting with people. Another one said it is inconsistency. Still another, incoherence.

There are those who think he should stick more to talking about the economy, and those who think he needs to broaden his emphasis to other issues, such as school vouchers, that motivate social conservatives.

An adviser, also speaking on the condition of anonymity, said he wished Romney would become more inspirational and less technocratic.

“Romney’s candidacy remains short on aspiration,” columnist Michael Gerson, who was former president George W. Bush’s chief speechwriter, wrote in Friday’s Washington Post. “His public appeal, at this point, is a combination of emphasizing his business experience, criticizing [President] Obama’s record and reassuring conservatives. This is a campaign — but not a cause.”

Murphy, on the other hand, thinks Romney needs to become more steely.

“We already have a president who is long on bromides and poetry but very short on hard-headed results,” Murphy wrote in the latest issue of Time magazine. “The country is in trouble, and voters know it. They are looking for something different: a tough yet honest coach who may cut the slowest players but who knows how to push hard, lead a team and bring home the championship.”

But others dismiss such criticism as carping from the sidelines, and panic over the latest sign that some other contender might be emerging as a threat.

“Anytime a poll comes out and shows you behind somewhere that people think is important, some of your supporters go, ‘Oh my gosh, you’d better change something,’ ” said Charlie Black, a veteran Republican presidential strategist and Romney supporter. “But from what I see and hear, I would not recommend any changes to what he’s doing.”

Those who are on the campaign payroll, meanwhile, say they have no intention of making any.

“We feel that things are clicking for us,” said Eric Fehrnstrom, a top adviser. “For us, it’s steady as she goes.”

The candidate begins most mornings with a conference call with his two main message mavens, chief strategist Stuart Stevens and Fehrnstrom, and nearly a dozen other senior aides to discuss new lines for the candidate to try. Meanwhile, top supporters, including New Jersey Gov. Chris Christie, call frequently with suggestions, while other friends and advisers e-mail him their thoughts.

All of that advice doesn’t always come out cleanly, said one senior adviser, who spoke only on the condition of anonymity.

“He’s got all the pieces up there and lets the computer in his head sort out what’s going to fit into what slot at any given moment,” the adviser said.

Before business-oriented audiences, Romney seems at ease, focused and assured, a man who knows he is talking a language his listeners understand.

“In the private sector that you all live in, you’re either fiscally conservative, or you’re out of business,” Romney told a Chamber of Commerce lunch in Farmington Hills, Mich., on Thursday. “How is business different from government? There are a lot of differences. One is your job is harder. There’s no question being in the private sector is very demanding and less forgiving. You see, in government if you make a big mistake, you just blame the opposition party.”

But when he takes the stage at large rallies without a teleprompter, Romney veers from bromides about America’s greatness (“I love America. I love its beauty. This is a beautiful state, too. I love this state.”) to odd facts about his upbringing (“My dad was a lathe and plaster carpenter, like a drywall carpenter. He could take a handful of nails, stick them in his mouth and spit the nails out pointy end forward.”) to broad indictments of Obama (“The president is slowly but surely turning us into a European-style welfare state. This is not the America we’ve known.”).

Romney’s word choices — such as his recent declaration that he had been a “severely conservative” governor — can grate on the very people he is trying to win over.

To hear him, it would seem that there is no problem in Washington that would not be solved by firing the chief executive. And when he expresses empathy, it is generally reserved for entrepreneurs starving for capital and bankers so burdened by the new Dodd-Frank financial regulations that they have to hire hundreds of lawyers.

Nor does he suggest that fiscal discipline involves much by way of pain.

Romney promises to bring federal spending down to 20 percent of GDP from the current 24 percent, by eliminating every federal program that isn’t necessary. But the only specific cuts he mentions are the relatively small savings that would be obtained by ending federal subsidies to Amtrak, the National Endowment for the Arts and the National Endowment for the Humanities.

Those who are eager to see Romney improve and sharpen his message will be watching closely next Friday, when he makes a much-anticipated speech before the Detroit Economic Club, just four days before the Michigan primary. Interest in the speech is so great that the club has moved it from a hotel ballroom — which sold out in hours — to Ford Field, home to the Detroit Lions — a team that hasn’t won a championship since 1957.