Will tonight be a one knock-out punch? Probably not.
The Super Tuesday contests are headed toward a split decision, but the biggest election night on the Republican presidential calendar will set the course ahead for the nomination to face President Obama in November - and could mark the moment when Mitt Romney finally emerges as the GOP's all-but-inevitable choice.
For the former Massachusetts governor, a victory in the Ohio primary and a show of strength across the country would enable him to argue that he is the only contender with a realistic mathematical chance of claiming the 1,144 delegates needed for nomination. That's a case his campaign is poised to make Wednesday morning.
For former Pennsylvania senator Rick Santorum, winning in Ohio as well as the Sun Belt would weaken Romney's argument and demonstrate the resilient appeal of the social conservative champion against his opponent's superior organization and money.
For former House speaker Newt Gingrich, a victory in his home state of Georgia is necessary if he is to stay a viable candidate, and rivals say he needs to score elsewhere, too. And for Texas Rep. Ron Paul, winning any state, most likely the North Dakota or Alaska caucuses, would provide bragging rights as well as delegates.
"They're pretty high stakes," says former Republican National Committee chairman Ed Gillespie, who isn't affiliated with a campaign. Many in the party are ready to move past this fight and on to the next one, he says. "Republicans have reached a point where they're largely tired of Republican-on-Republican violence and are eager for a point at which a Republican nominee is making the case against President Obama rather than amplifying pretty minor differences between ourselves."
As the four candidates campaigned Monday from Alcoa, Tenn., to Zanesville, Ohio, statewide polls show Romney and Santorum tied in Ohio and Romney narrowing the gap in Tennessee - Tuesday's most critical battlegrounds.
Super Tuesday isn't as dominant as it was four years ago, when two dozen states held contests on Feb. 5, 2008. Then, a strong showing by Arizona Sen. John McCain essentially settled the Republican race, which had many winner-take-all contests. An almost even split between Barack Obama and Hillary Clinton fueled a long battle on the Democratic side, where party rules required proportional distribution of delegates.
Republican National Chairman Reince Priebus cites that Democratic example in dismissing angst about whether the GOP's prospects for winning the White House are being damaged. "The process on the Democrats' side went on until June and in the end they ended up doing pretty well," he says. "We are in the second or third inning of a nine-inning game."
The idea of grouping primaries on one high-stakes day was launched in 1988 by Southern Democrats who figured a regional primary would increase the odds the party would choose a moderate candidate rather than a liberal one. (It didn't work that year, when Massachusetts Gov. Michael Dukakis won the nomination, though in 1992 a Southern-flavored Super Tuesday did boost Arkansas Gov. Bill Clinton.)
This season's busiest election day includes contests in the Northeast, Midwest and West as well as the South. It has become a sort of national primary that has Romney fighting on all fronts as his three opponents pick where to make a stand.
"This year, it's not really big and not concentrated in one particular set of states," says political scientist John Green of the University of Akron. "The other way an event like Super Tuesday can have an impact is where it falls in the primary process. The process up to this point has been so volatile. ... From that perspective Super Tuesday is poised to determine whether the campaign starts winding down or accelerates."
The countdown starts with some givens. His rivals have ceded the Massachusetts primary to Romney, who served as governor there, and only Paul has made a noticeable effort in neighboring Vermont. Romney holds an overwhelming lead in Virginia, where only he and Paul filed enough signatures to get on the ballot.
Among the other seven states, there are tests of the ability of campaign organizations to turn out supporters for caucuses in Alaska, Idaho and North Dakota; a battle for the party's conservative base in primaries in Georgia, Oklahoma and Tennessee; and a showdown in Ohio, one of the country's quintessential swing states.
Some of the remaining questions in the GOP race will be answered by what happens. Here's what to watch for as the results come in tonight.
A week ago, Romney edged Santorum in Michigan, a victory in his home state that gave him only two more delegates than his challenger but amounted to a critical test of his campaign. Now they face off in neighboring Ohio, which has a similar political landscape with a slightly more favorable incline for Santorum.
For one thing, Romney doesn't have a home-turf advantage in Ohio, while Santorum is familiar in the eastern part of the state from his days as a congressman and senator just over the border in western Pennsylvania. What's more, Ohio has a larger share of the evangelical Christians and blue-collar workers who have boosted Santorum elsewhere.
"All eyes are going to be on Ohio, and it's a region that sets up well for Santorum," says Stuart Roy of the super PAC supporting Santorum, the Red White and Blue Fund, which is spending half a million dollars on TV ads in the state. "We don't view any single state as must-win, but clearly Ohio is very important."
On Super Tuesday, Santorum needs to win "a few states" while Gingrich "teeters off to irrelevancy," Roy says. "Then we have a true two-man race, and that's the game change."
Rich Beeson, Romney's political director, calls the Ohioprimary "a knife fight in a phone booth" - that is, a close and hard-fought contest he says is a must-win for Santorum. "If he doesn't win Ohio, it's hard to see how his momentum and money stick around long enough" to challenge Romney in the big states that follow, such as California and New Jersey.
"We want to win as many delegates as we can on Tuesday," Beeson says of the Romney campaign's goals, "and ideally on Wednesday ... we can lay out a pretty strong case on why it's going to be mathematically impossible for Rick Santorum to get the nomination."
Organizational missteps have hurt the drive for delegates by the Santorum campaign, which failed to file delegate slates in three of Ohio's congressional districts.
Math is Romney's friend, says political scientist Josh Putnam, who tracks the political calendar on a blog called Frontloading HQ. "At some point, when it's apparent he's the only one who can get to 1,144, that's when we start seeing the internal calculations within the other campaigns: What's the use of continuing on if we're just kicking the can down the road and hurting our potential nominee?"
Gingrich: Can he come back again?
Gingrich has been stumping in Georgia like a candidate for local office, making what could be a last stand in the state he represented for two decades in Congress. "I have to win Georgia, I think, to be credible in the race," he acknowledged to business leaders last week. When Romney was struggling for traction in Michigan, Gingrich said any candidate who failed to win his home state would be "very, very weakened."
Statewide polls show Gingrich with a double-digit lead as Romney and Santorum battle for second place. But not everyone thinks a win in Georgia alone will be sufficient to make Gingrich a credible contender again.
"At some point he's got to win something out of the South and show he has a sustained campaign," says Beeson. Roy says Georgia is Gingrich's "floor" - that is, the minimum he has to do.
Still, Gingrich notes to almost every audience that he's been counted out before, only to surge in Iowa and then again in South Carolina, where he won the primary. "I keep coming back," he said wryly Sunday on NBC's Meet the Press.
He signaled his intention to stay in the race by sending a campaign schedule to reporters that showed him campaigning in Alabama on Wednesday, Mississippi on Thursday and Kansas on Friday.
Both the Gingrich campaign and a pro-Gingrich super PAC, Winning Our Future, have bought time for TV ads in Alabama and Mississippi. "Since Barack Obama's inauguration, gas prices have doubled," the campaign ad declares, then foresees a Gingrich administration. "They can go down under the Newt Gingrich $2.50-per-gallon plan."
Paul: Can he win somewhere?
Let others battle in the population centers of Ohio and Georgia. Ron Paul is focused squarely Tuesday on wide open spaces - in Alaska, Idaho and North Dakota, which hold caucuses that favor his band of loyal supporters.
"Our focus is to win a majority of the delegates to county and state conventions coming out of the caucuses," says campaign strategist Jesse Benton. "We believe we have a strategy to cover a very sizable chunk of delegates."
Paul's methodical campaign is trying to gain enough delegates to win concessions in the party platform and increase influence in the GOP for his proposals to limit the power of the Federal Reserve, return the nation's currency to the gold standard and curtail military and other entanglements overseas.
The campaign also would like to win a state, a goal it narrowly missed in Maine's caucuses last month. North Dakota and Alaska are his strongest prospects. In recent days, the campaign has sent reporters photos that show crowds estimated at 1,000 and more greeting him in locales including Sandpoint, Idaho, and Fairbanks, Alaska.
"We are confident that he will be an active candidate until the convention," Benton says, though he adds, "If there were a scenario where one of the other candidates did win clear and free 1,144 delegates, that's the time to reconsider."
Romney: Can he woo the base?
Romney has come from behind to win the two most critical primaries to date, in Florida and Michigan, helping him recover from setbacks in other contests.
Still, surveys of voters as they left polling places in both states showed first Gingrich and then Santorum carrying the lion's share of the party's most enthusiastic supporters: Evangelical Christians, strong Tea Party supporters and those who call themselves very conservative.
"You could have a situation where Romney ends up only winning his region of the country," in Massachusetts and Vermont, Roy says. (He discounts Virginia because Santorum and Gingrich aren't on the ballot.) He calls Romney a tough sale to the GOP base. "I'm originally from Mississippi, and Massachusetts isn't really popular there."
One Super Tuesday test is whether Romney can woo and win those voters.
He's making progress by waging the battle Republican voters wanted to see, Beeson says. "They didn't want a coronation. They didn't want somebody to get it because it's their turn. They wanted somebody to fight for it and earn it, and that's what he's done."
On Sunday, Romney was endorsed by Oklahoma Sen. Tom Coburn, the most conservative member of the Senate in National Journal ratings, and House Majority Leader Eric Cantor, a Tea Party favorite. Former first lady Barbara Bush recorded a robocall urging Ohio voters to support her friend "Mitt."
Putnam says he'll be watching whether someone can "win out of their comfort zone." Gingrich needs to show he can carry a state outside the Deep South, for instance, while Romney needs to demonstrate he can win in that region.
Whatever happens on Super Tuesday, he'll have another test of that soon. Next week's primaries: Alabama and Mississippi.