The Republican presidential primary race just entered its March madness moment. Until now, contests have come mostly one at a time, with a couple of notable exceptions in February where two or three states held primaries or caucuses in the same week. And for all the hyperventilating and hyperfocus on the race, only 172 delegates have actually been allocated to the candidates, and it takes 1,144 to win the nomination. Mitt Romney has the most delegates at this point with just 118, or about a tenth of what he needs to lock it up.

All of that changes today. Ten states hold nominating contests, seven of which are binding primaries. The spread of states reaches from a caucus in Alaska to the primary in Georgia, testing the logistical and organizational strength of all four remaining GOP candidates. At stake in the seven primaries are 350 delegates, all of which will be proportionally allocated depending on the results. A big enough overall victory could propel one candidate to a bandwagon moment and bring the race to an early close. A closer contest could break the race wide open and keep candidates fighting into June — or perhaps to that political pundit's fantasy, a brokered convention.

Santorum needs to win Ohio, a middle-America, Rust Belt state where his emphasis on blue-collar economics should find the most resonance.

Conventional wisdom would have Romney doing very well, thanks to superior organization and timing — and in this case, conventional wisdom may get it right. Romney did well in the final debate of the nomination process on February 22 in Arizona, and Rick Santorum's defensive performance has deflated his standing in the polls. Romney won both the Arizona and Michigan primaries a week ago, and added two caucuses in Wyoming and Washington later in the week, the latter by a surprisingly large margin. Neither caucus bound any delegates to Romney, but the momentum and media coverage have shifted in his favor, just in time for the toughest day of the race.

The Super Tuesday schedule also favors Romney. He should get an overwhelming victory in Massachusetts, his home state, where no other candidate has seriously competed for the 41 delegates. The same is true with Vermont and its 17 delegates. Virginia should have been competitive, but neither Newt Gingrich nor Santorum qualified for the ballot in the Old Dominion, and a majority-vote win over Ron Paul would allow Romney to claim all 49 delegates. That gives Romney a big springboard toward winning a majority of the delegates at stake today.

Still, Gingrich has a firm grip on the biggest prize today. His home state of Georgia has 76 delegates, and Newt enjoys a double-digit polling lead over Romney and Santorum. Getting a majority of Georgia delegates would more than double Gingrich's current 29 bound delegates, but still leave him far behind Romney for the nomination. Gingrich remains competitive in Tennessee, but the most recent polling has him in third place, and Gingrich isn't competitive in Ohio or Oklahoma, the other two primaries taking place today.

Santorum has a better opportunity to slow Romney down and extend the race. Oklahoma has 43 delegates up for grabs, and Santorum has a big lead in the polls — although no surveys have been conducted since the Arizona debate. If Santorum can maintain that big lead in Oklahoma, he can get a significant haul of delegates. But if Romney can ride the Sunday endorsement of Sen. Tom Coburn to a boost in the state, that delegate allocation could become a wash. In Tennessee, Santorum still has a small edge and could get a majority of the state's 58 delegates.

Of course, Oklahoma isn't really the critical state for Santorum. He needs to win Ohio, a middle-America, Rust Belt state where Santorum's emphasis on blue-collar economics should find the most resonance. Like Michigan, Santorum ran up big polling leads in Ohio in mid-February, only to lose them as the actual primary contest approached. Polling in the last 48 hours shows Ohio as a toss-up. A narrow win won't help Santorum outside of the psychological edge, either, as his organizational difficulties last year left him unable to compete for as many as 18 of the state's 66 delegates. Depending on which congressional districts he wins and loses, a small popular-vote win statewide for Santorum might still result in Romney winning a significantly larger number of delegates.

Most eyes will stay on the results in Ohio and Tennessee tonight. If Santorum can hang on and win both those states, he will still trail Romney in delegates (and possibly Gingrich as well), but will convince donors to keep funding his campaign as the best alternative to Romney. If Romney edges Santorum in either state — but especially Ohio — Santorum has a difficult sale to make on his continued presence in the race. Primary campaigns usually hit a tipping point where Republican voters and donors begin to flock to an undisputed leader in order to bring the fight to a quick conclusion. If Santorum can't keep Romney from claiming to be that undisputed leader on Super Tuesday, he may exhaust the patience of both groups.