After months of anticipation, Scott Brown finally made it official last night in Portsmouth, N.H.: He’s running for the U.S. Senate against incumbent Democrat Jean Shaheen.

"I want you all to know about a decision I’ve made," he told the crowd. "Starting today, I am a candidate for the United States Senate for the state of New Hampshire."

During his 20-minute campaign kickoff speech, Brown made it clear that he sees Shaheen’s support for the Affordable Care Act as an unforgivable sin.

"So many problems with our country and the economy happened, and continue to happen, because of everything that’s related to Obamacare," he said. "And you need to remember — it’s so critically important that you remember — that this never would have happened without the rubber-stamp yes vote of Sen. Shaheen."

Brown also went out of his way to stress a politically crucial point: Even though he only moved to the state recently, his New Hampshire roots run deep.

"When my mom was young, she was a waitress at Hampton Beach," he said. "And my dad was an airman at Pease Air Force base, and they met, they fell in love, and about a year later they had me. And I’ll tell you, when they carried me home, it wasn’t too far from here. It was a house right over on Islington Street."

Of course, New Hampshire isn’t where Brown’s political career took off. Four years ago, Brown was a little-known state senator in Massachusetts, waging a seemingly doomed battle for the U.S. Senate seat formerly held by Ted Kennedy. But then, after campaigning as the 41st vote against the Affordable Care Act, Brown won — sending shock waves through Washington.

"This senate seat belongs to no one person, no one political party," he said at the time. "And as I’ve said before, and you’ve heard it today, and you’ll hear it loud and clear — this is the people’s seat!"

That victory turned Brown into one of the biggest names in the Republican Party. But the magic didn’t last: Less than two years later, Brown was roundly defeated by liberal darling Elizabeth Warren. Even on election night, though, Brown was hinting at a comeback.

"There are no obstacles you can’t overcome," he said in his concession speech. "And defeat — and defeat is only temporary."

Compared with Massachusetts, where the GOP is in danger of becoming a nonfactor, New Hampshire could be fertile ground for Brown’s brand of populist moderate Republicanism. But that moderation could also be a liability. Outside his kickoff, Keith Mistretta of Durham cited Brown’s support for some gun control measures as a reason he would never support him.

"Scott Brown is far too liberal to be in the Republican Party," Mistretta said. "He voted 62 percent of the time with the Democrats. He voted against our Second Amendment multiple times. For example, he votes to limit against magazines in guns."

Another question is what lessons Brown took from his loss to Warren. As a rule, Brown’s low-key affability is one of his great political assets — but during that race, Warren seemed to get under his skin.

According to the polls, Brown currently trails Shaheen by a substantial margin. Of course, if recent history is any indication, running as an underdog is what Scott Brown does best.