Former Senator Rick Santorum announced Tuesday that he would suspend his campaign for the presidency, leaving a clear path for former Massachusetts Governor Mitt Romney to assume the Republican nomination and challenge President Barack Obama in November’s election.

Even though the Republican national convention will not take place until August, Harvard professors said that Romney has nothing between himself and the nomination. Both Romney and the president are Harvard alumni—Romney from Harvard Business and Law School, Obama from just the Law School—making the race the first between two Harvardians since 2000.

“[Romney] technically doesn’t have enough delegates yet,” Institute of Politics director C.M. “Trey” Grayson ’94 said, but “there’s no political scenario that would create any other outcome than a Romney nomination.”

As he began to pull away in the race for delegates in recent weeks, Romney already had begun to shift his focus to the general election and Obama. Professors said Romney is likely to regroup further as the Republican primary season draws to a close in the coming months, better tempering his campaign and its message for the fall.

“I would think that he’s going to shift into a prolonged media and fundraising tour, and he’ll use the completion of the primary cycle as an extended series of victory laps,” said Harvard Kennedy School lecturer Richard Parker. “He’ll use the process of seeming to campaign to test messages.”

A key part of that message will inevitably be choosing a running-mate, but it will also be setting the tenor of the race. Professors said the match-up between the former Massachusetts governor and the president will likely have a different focus than the Republican nominating race.

“Campaigns seek to mobilize their core supporters and appeal to those who are undecided or persuadable. In doing so, they emphasize those issues and themes that are uppermost in the minds of voters and those issues that play to their strengths,” Harvard Kennedy School professor Roger B. Porter wrote in an email.

As things stand, the theme this time around will likely be the economy, professors said.

“I think the key thing is [Romney’s] got to continue to focus on the economy,” Grayson said. “He’s got to do a better job articulating what is Mitt Romney’s vision for the country. It’s going to be a right of center message.”

In his exit speech on Tuesday afternoon, Santorum declared “we are not done fighting” and that he would continue to help defeat Obama. The support for his party fell short of directly endorsing Romney.

The former Pennsylvania senator dropped out just two weeks shy of his home state’s primary, which political experts have begun to suspect could go to Romney. Though he did not definitively name a reason for dropping out, Santorum had recently taken a few days off from the campaign trail to care for his sick daughter and re-evaluate his campaign.

“Those who seek elective office are by and large realists. Rick Santorum...eventually concluded that [his] window of opportunity had passed,” Porter wrote. “Contesting the battle further was expensive and potentially damaging to [his] brand.”

Fellow Republican contenders Newt Gingrich and Ron Paul have pledged to stay in the race, but experts said that their candidacies are now more about spreading a message than actual electoral ambition.

—Staff writer Nicholas P. Fandos can be reached at nicholasfandos@college.harvard.edu.