Mitt Romney's impressive victory Tuesday makes it very likely that we will look back on the Florida primary as the contest that determined the 2012 Republican nomination.
To be sure, the campaign fight will go on, and Romney is by no means assured of a sweep of the relatively few February contests.
Newt Gingrich has vowed to run all the way to the convention, whatever the odds. He has shown similar determination in the past.
He ran and lost twice for Congress before he was first elected in 1978. He saw his party lose seven straight elections for the House before he led it to its first majority in 40 years in 1994. Gingrich sees himself as a world historical figure, whose destiny should not be forestalled by a few weeks of negative ads and a couple of subpar debate performances. He's also pumped up by anger.
Rick Santorum has shown similar determination, in Pennsylvania and in this cycle. He made hundreds of campaign appearances in Iowa, New Hampshire and South Carolina with no perceptible impact in the polls until he hit double digits in Iowa at Christmastime, two weeks before the caucuses. Santorum sees himself as a principled leader, unafraid to take political risks.
It would be severely out of character for either to withdraw. And neither has any other commitments on his calendar.
As for Ron Paul, he believes, not without cause, that his message of abolishing the Federal Reserve, legalizing marijuana and withdrawing from much of the world has been gaining resonance and attracting followers. He doesn't expect to be president anyway, so why not take advantage of this chance to get the message out even more?
The first February contest is the Nevada caucuses on the fourth. Romney won easily four years ago, thanks in part to the high turnout of his fellow Mormons. But the Nevada caucuses had never been held before, and turnout was a low -- 44,000 in a state of 2,700,000 people.
It's likely to be higher this time, with a lower Mormon percentage, and in a state where Republican primary voters chose Sharron Angle in 2010.
The Maine caucuses start, but don't finish, on Feb. 4. Romney forces are confident there, but Maine Republicans nominated and elected a very conservative governor in 2010.
Three days later, on Feb. 7, come the caucuses in Minnesota and Colorado. Romney won both in 2008, when he was the only Republican candidate with much of a caucus organization.
Maybe not this time. In state elections, Minnesota Republican caucus-goers have tilted far to the right, with many strong right-to-lifers -- a group more likely to favor Santorum or Gingrich than Romney. Colorado's caucuses have a lesser conservative tilt and look pretty safe for Romney.
Those caucuses are non-binding; so is Missouri's primary on the same day. Missouri was a tight three-way race last time, and Romney did well in the two big metro areas that cast about half the vote. Gingrich is not on the ballot, so Santorum has a chance to shine in the rest of the state where Romney ran weakly.
Finally there are the Michigan and Arizona primaries on Feb. 28. Michigan is Romney's native state, where his father was elected governor when he was in 10th grade, and he won there in 2008.
A Michigan poll taken in the days after South Carolina showed Romney leading Gingrich by only 5 points. There's no recent polling in Arizona.
Many analysts see February as a Romney sweep month. I'm not so sure. We may see among Republicans a phenomenon apparent in the 1980 and 1992 Democratic cycles: When a candidate who is not hugely popular seems to have a nomination clinched, people with qualms start voting for whoever else is still campaigning.
Romney is seeking to lead a party fired up by opposition to the Obama Democrats. He has campaigned with a feisty spiritedness that is at odds with parts of his record and often with his temperament.
He has succeeded in large part because the only ideologically pure candidate, Michele Bachmann, lacked stature, and his more experienced rivals lacked purity.
In Florida, Romney showed fire, drive, energy and a willingness to attack, and carried just about every segment of the electorate. Unlike his rivals, he has maintained competitive general-election numbers in this largest of target states.
Florida provided a benchmark win, but more tests lie ahead.