(Charles Dharapak/AP Photo/Pool)

Mitt Romney lost far more than South Carolina last night.

He also lost the air of inevitability around his candidacy. Newt Gingrich beat Romney in decisive, sweeping fashion in a state with a long history of picking winners - cutting into Romney's strengths on economic issues and even on the question of electability, a critical attribute in a year Republicans desperately want to defeat President Obama.

But just because South Carolina voters consider Gingrich to be electable doesn't make that so - not even, necessarily, in the Republican primary.

The race gets harder from here for Gingrich. First up is Florida Jan. 31, an enormously expensive state to advertise in.

Romney is already up on the air in the Sunshine State, and the Romney campaign's organizational and financial advantages mean he's already been banking early and absentee votes.

The two debates this week in Florida, coupled by publicity from his South Carolina victory, are likely to help Gingrich vault into quick contention. But Romney and his allies won't be holding back in defining Gingrich and highlighting his breaks with conservative dogma, and Romney is poised to put issues of his tax returns behind him after stumbling over the issue last week.

After Florida, the campaign essentially goes national. The February caucus states, scattered from Nevada to Maine, are where Romney's organization and fundraising prowess start to matter.

It's worth remembering that while Romney had a chance to end the campaign early if he'd won South Carolina, his aides have always prepared for a slog of a fight to the nomination.

Yet there's a deeper reason for the Romney campaign to worry. Gingrich is succeeding by plucking emotional chords with the Republican base - notes that Romney has famously been unable to match, and the type of music that has a way of plowing over grass-roots organization and slick ad campaigns.

Gingrich capped an astounding comeback by winning South Carolina after falling far back in the pack in Iowa and New Hampshire. His candidacy was declared effectively dead at least twice before he roared back into contention.

Romney remains the frontrunner by any objective criteria. But those same traditional ways to measure campaigns strongly suggested that Gingrich would have been forced out of this race long ago.

So the campaign moves on with Romney displaying more vulnerabilities than were evident just a few days ago. Gingrich, meanwhile, is connecting with voters in a way that Romney never quite has.

A race that was close to being effectively over by now will linger for weeks or, more likely, months. That's particularly true if Rick Santorum pledges to stay in the race, as he said he would do on ABC's "This Week" today.

A long nomination fight probably helped President Obama as a candidate four years ago. But he'll gladly take an extended battle on the other side this time, with Romney and Gingrich doing damage to each other that he'll be happy to pick up on in the general election.

The preferred choice of candidates at Obama's Chicago campaign headquarters remains Gingrich. His well-documented flaws has prominent Republicans worried about the impact he'd have on congressional candidates in November, and those concerns will grow louder if Gingrich looks like he has a plausible shot at the nomination.

Democrats are still training their fire almost exclusively on Romney, hoping to soften him up further and boost Gingrich's prospects.

But this latest stretch shows that the former House speaker has extraordinary political durability. His unique brand of campaigning, crafted by a man with a unique mind, is working.