After reemerging at the front of the Republican primary race last week, Mitt Romney’s campaign suffered a major setback Tuesday night in the shadow of Sen. Rick Santorum’s sweep in three state primaries—contrary to the predictions of many Harvard experts.

Santorum was met with a flood of support in Minnesota and Missouri, winning 45% and 55% of the vote, respectively. He also eked out a narrow victory in Colorado, a state Romney carried decisively in 2008, leading the former Massachusetts Gov. by five percent.

Romney struggled to garner even a quarter of the vote in Minnesota and Missouri.

Yet as recently as last week, Santorum’s campaign looked to be all but over, having failed to win a single contest since narrowly taking the Iowa caucuses last month.

Santorum’s position as the conservative alternative to Romney appealed to voters in Missouri’s non-binding contest, political experts said, but Romney was expected to carry Minnesota and Colorado.

Romney’s disappointing showings come after two impressive primary contest victories last week, which placed him firmly in the front of the Republican pack. His nomination, Harvard professors said, was all but inevitable.

“He’s clearly winning,” said Harvard Government professor Theda R. Skocpol on Tuesday afternoon. “It’s not like a home run clearing the fences. It’s more a series of dropped balls and singles, but he’s winning.”

Last week’s surge had enabled the Romney campaign to turn its focus towards the general election. In speeches and press releases last week, Romney increasingly called into question President Barack Obama’s record and positioned himself as the logical alternative to the current administration.

Yet despite his losses, Romney continued his attack on Obama in a speech in Colorado following the primary, telling a crowd of supporters that he would still be their nominee.

“Romney people have been assuming that they would run as the people who know how to fix the economy Obama has bungled,” Skocpol said. “I think it’s fair to say that the Republican primary electorate is settling for Romney, but it’s not excited about him.”

Like Skocpol, Harvard Republican Club president Derek J. Bekebrede noted that Romney’s attempt to position himself as the presumptive nominee leaves much to be desired.

“The fact that you’re inevitable doesn’t make you inspiring,” Bekebrede said.

Romney’s trouble on Tuesday underscores the questions that have dogged him as his campaign gained momentum, including scrutiny of his business credentials and personal finances.

According to Harvard professors, that negativity has left Republicans, and particularly Romney, battered and wanting for energy as they emerge into the general election.

“Unlike most of the nominees who have come out of either party in recent memory, he’s pretty messed up,” Kennedy School Lecturer Marty A. Linsky said. “He’s been beaten up pretty badly.”

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