This wouldn't have even been an option for Brown were New Hampshire Republicans not in such disarray. But all of the highest-profile potential GOP candidates long ago gave up the idea of running against the well-funded and reasonably popular Shaheen, leaving a big opening. Brown, though, is as Boston as they come, so he's gone to great lengths to emphasize his thin Granite State ties. Amusingly, he once even called New Hampshire "a second home" because he was "born at the Portsmouth Naval Shipyard"—which is actually located in Kittery, Maine.
To solidify his standing, Brown and his wife relocated to New Hampshire, where they'd owned a vacation house, and sold their Massachusetts home late last year, all while claiming the move was for "strictly personal" (and not political) reasons. This sort of drawn-out game-playing wore very thin on local Republicans, who longed for a clear answer from the prevaricating Bay Stater, but undoubtedly all will soon be forgiven, because it's not like they have any better choices.
But can Scott Brown actually win? He certainly has strong name recognition; much of New Hampshire is in the orbit of the Boston media market, where he was always prominent during his short Senate tenure. And he's also a prolific fundraiser, so even with a late start, he shouldn't have trouble raising money. The polling, however, has been somewhat mixed and variable: In January, for instance, PPP showed Shaheen with just a 3-point lead, but last month, that had widened back out to 8 points. A couple of other recent surveys have found Brown back by double digits.
And, of course, there's the dreaded carpetbagger label. Sometimes it can prove deadly to a campaign, but often its importance gets exaggerated. New Hampshirites can be a bit prickly about their identity, though, forever in the shadow of their larger neighbor to the south. And while committed Republicans are apt to overlook Brown's origins, some independent voters (who make up the largest contingent of the New Hampshire electorate) may not feel as charitable. Indeed, Democratic allies have already run ads slamming Brown for "shopping for a Senate seat," suggesting that this may be a potent line of attack.
One thing is certain, though: At the very least, assuming Brown follows through on this whole "exploratory" business, Shaheen will have to work much harder than she would have against any of the Republican also-rans considering this race. And it's also possible that national Democratic groups will have to spend money on New Hampshire that they otherwise didn't anticipate having to spend. That will make life tougher for Democrats nationally, given that the party already faces a very difficult set of elections across the country on which control of the Senate depends.
But Scott Brown isn't running just to take one for the team. He almost surely has polling showing him with a path to victory, and this exploratory committee is very probably just some more kabuki, since he's unlikely to jump this far in only to jump back out (though you never know). Shaheen remains the favorite, but this won't be easy if Brown commits, and Democrats will have to remain vigilant in order to keep this seat blue.