MANCHESTER, N.H. - Rick Santorum's transition from scrappy Iowa underdog to national contender hit some bumps in his first full day campaigning in New Hampshire since his near-upset in the Hawkeye State.

At the first stop we covered today, at the Merrimack train station in Northfield, N.H., the former senator from Pennsylvania charmed the crowd, telling his life story, making his pitch and winning them over. Diving into the traditional engagement that New Hampshire voters demand, Santorum excelled in the back-and-forth.

But at the New Hampshire College Convention, at the Grappone Conference Center in Concord, N.H., he seemed lecturing and occasionally prickly. And while perhaps an instructive tone is not entirely inappropriate in front of students, he did some of the same Wednesday night at a senior center in Brentwood, N.H.

His debate with college students about same-sex marriage grew contentious.

"Why shouldn't marriage [be] between three men?" he asked at one point.

His position on the issue is one that certainly will have appeal for the social conservatives in this state, where same sex marriage is legal, and even more so for his next audience in South Carolina. But the extensive back-and-forth - he clearly relishes debate - distracted from his task at hand: introducing himself to voters, explaining his rationale for his candidacy, and becoming a contender. While his bona fides as a social conservative are part of that, his task is to now expand beyond those base Republican voters. Even before that debate over marriage, Santorum's stump speech was long on history lessons, short on rallying supporters.

Santorum, at one point, asked for a show of hands as to who knew the national motto. He expressed a shocked disgust that "only 5 percent of you are raising your hands."

Moreover, he was wrong. He said the motto was "E Pluribus Unum." It isn't. It's "In God We Trust" - as Republicans pointed out two months ago in a House resolution  after President Obama made the same mistake.

Presidential campaigns provide opportunities for candidates to grow and mature, to step into the role of a national leader. Not every candidate is able to meet the moment - witness Howard Dean, for example, or Mike Huckabee. Sometimes the thinking is: Well, this worked for me up until now, so I might as well continue doing it. But that is a fallacy. Campaigns are opportunities to grow into something else. No nominee starts the same as he ends.

Santorum will need his campaign to grow in infrastructure, fundraising, endorsements and national reach. After New Hampshire, as the candidates move to states that depend less on retail politics and more on money, TV ads and major rallies, this will become a resource war.  But that won't be enough. He will need to grow, as well.

Conservatives are looking for a candidate around whom they can rally. Santorum will need to rise to the occasion, or like others before him, he could fall.