Front-running candidates like to imagine a path to victory if only they run the race as they envision. On the wind-swept farm from which he launched his presidential campaign here Thursday, Mitt Romney no doubt hoped that will be the case.

But like all front-runners, no matter how strong or fragile, Romney’s struggle will be trying to stay on the course he has set, to run his race and not the race that his rivals and others attempt to make him run.

Can he make this campaign all about the economy and President Obama’s stewardship in office? Or will he find himself in constant conflict over his Massachusetts health-care mandate, his conservative credentials, his “authenticity” and questions about whether he can connect with and truly rally the entire Republican Party?

Romney begins his second bid for the White House in far stronger shape than he started his first one four years ago, with a plan and a message sharply honed and more narrowly focused. He is better positioned than his rivals, and more experienced, too. It is an enviable but hardly an impregnable position, given the questions that surround him and the narrowness of the margin in the polls atop which he sits.

His message Thursday was pitched more to a general-election audience than to his party’s base, which is a page from successful candidates. Boiled down to four sentences, it went like this: “Barack Obama has failed America. When he took office, the economy was in recession. He made it worse. And he made it last longer.”

That’s the message he wants to carry through the nomination battle, if only it were that simple.

Romney’s front-running status owes as much to his prowess as a fundraiser as to the depth and breadth of his political support. He is capable of raising more than $10 million in a single day, a prodigious achievement. He threatens to leave his rivals in the dust at the end of this quarter in money raised and banked. That is an enviable position.

Yet he is a front-runner who must still decide whether he can risk anything approaching a serious effort in the Iowa caucuses or how he will maneuver in South Carolina. He and his advisers can try to dismiss the Iowa contest as not truly representative, even of a conservative party. Iowa will not decide the nomination, but his position speaks to one of the vulnerabilities he carries at the start of his race.

Romney and his advisers know that presidential campaigns are won in the middle and that nomination battles are a series of continual choices between catering to the base and keeping the center squarely in view. New Hampshire, where he announced, is obviously a must-win for the former Massachusetts governor, and it is the place where his advisers think the center of the electorate, in the form of thousands of independents, will assert itself in the GOP nominating contest.

His Republican rivals may acknowledge Romney’s leading position in the race, but they are showing him little respect. Former Alaska governor Sarah Palin arrived in New Hampshire as Romney was breaking camp after his announcement, crowding a stage that should have been his alone. Reporters asked Romney about her pending arrival as he worked the crowd before his speech. “New Hampshire is action central today,” he said. “I love it.”

Palin’s bus tour, she has insisted all week, is decidedly not a political event. But the closer she came to New Hampshire, the more it took on the trappings. On Wednesday night, the Manchester Union Leader’s John DiStaso reported that Palin’s team had reached out to some conservatives to invite them to a clambake Thursday night.

Earlier Thursday, while touring in Boston, she took a poke at Romney over health care. “In my opinion, any mandate coming from government is not a good thing,” she said. She also gave a preview of what Romney’s rivals will do going forward, which is to raise doubts about his connection to the party’s new corps of activists, saying it will be a big “challenge” for him to appeal to the tea party forces.

Nor was Palin the only one crowding Romney on his announcement day. Hours before Romney spoke, the budding campaign of Jon Huntsman Jr., the former Utah governor, sent out an e-mail attacking Romney’s record. Huntsman arrives this weekend for another round of testing the waters, already warming to the coming competition with the front-runner.

As if that weren’t enough, Rudy Giuliani, the former New York mayor, was also in the state Thursday, raising money for New Hampshire Republicans as he put out the word that he is again thinking about running for president.

None of this particularly concerns those on Romney’s team. As they mingled with supporters and reporters on the farm of Doug and Stella Scamman in the hours before Romney’s announcement, they maintained that they have set their course without regard to whether Palin — or perhaps anyone else — becomes a candidate. Which is what they should say and what they should hope will be the case.

They expect attacks. And as veterans of the 2008 campaign, they know well the enthusiasm that Romney’s rivals brought to that task — and he wasn’t in as strong a position then as he is now. The field cornered Romney in a series of battles that ultimately allowed John McCain to find a path to victory. Romney will be every bit as much the focus of their attacks this campaign, once real engagement begins.

Republican nominees in many campaigns have started as heirs apparent. Romney is in a different position. If he wins the GOP nomination, it won’t be because it was his turn as the beloved senior Republican in the race. If he wins, it will be because he earned it, not just by running the campaign he hopes to run but also by preventing his rivals from dictating the battle on their terms.