Mitt Romney won a "hard-fought" victory in Michigan Tuesday night, but he won't have much time to celebrate. On March 6, "Super Tuesday," 10 states hold their primaries or caucuses, handing out more than 400 delegates — more than in all the presidential nominating contests combined so far. "Super Tuesday is going to be a huge, huge day," Rick Santorum told an enthusiastic crowd in Tennessee this month. His three remaining rivals agree, as do the pundits. Here, a guide to what happens on Super Tuesday, and what to watch for:

Which states are voting on March 6?
Alaska, Idaho, and North Dakota have Super Tuesday caucuses, and Georgia, Massachusetts, Ohio, Oklahoma, Tennessee, Vermont, and Virginia are all holding primaries. Among the 10 states, 413 delegates are up for grabs, with the big prizes being Georgia (76 delegates), Ohio (63), Tennessee (55), and Virginia (46). The states collectively have another 24 uncommitted delegate slots, reserved for Republican National Committee members.

Which race will people be paying closest attention to?
Ohio "has quickly become the highest-profile match-up of Super Tuesday," says Aaron Blake at The Washington Post, billed as a Midwestern rematch of the Michigan primary fight, which Romney won by 3 percentage points. Ohio and Michigan have similar demographics, but Ohio is neutral territory — Romney has deep Michigan ties — and Santorum currently leads in the polls. Romney's super PAC has already spent $2 million in the Buckeye State, to Santorum's half a million. "Ohio carries enormous symbolic weight both as a general election bellwether and a Republican proving ground," says Peter Hamby at CNN. It "will test each candidate's ability to connect with GOP voters of all stripes."

What other states are important?
Georgia is essentially Newt Gingrich's last stand: He's making a big play for his home state, and also trying to hit the jackpot in Tennessee, Ohio, and Oklahoma, with his super PAC, Winning Our Future, putting down $1.75 million in TV and radio ads attacking Romney and Santorum in those states. Virginia is another key swing state, but only Romney and Ron Paul made it on the ballot. Paul is focusing on the caucus states.

Will Super Tuesday finally decide the GOP nominee?
No. In past elections, Super Tuesday states awarded delegates on a winner-take-all basis. But with states dividing up their delegates proportionally this year, "no clear-cut winner will emerge" on March 6, says Christopher Rowland at The Boston Globe. Instead, "the quest for the 1,144 delegates needed to clinch the nomination now depends on strong finishes, not necessarily wins, in as many states as possible."

Which candidate is favored on Super Tuesday?
It's a fool's game to make predictions in this topsy-turvy race, says Liz Halloran at NPR. But currently, Santorum is polling well in Ohio, Oklahoma, and Tennessee; Romney is dominant in Massachusetts, Vermont, Idaho, and, almost by default, Virginia; Gingrich has a fading 9-point lead in must-win Georgia; and Paul has a shot at finally winning a state, either North Dakota or Alaska. 

What else should we watch for?
"We're looking at who can win outside their comfort zone," political scientist Josh Putman tells NPR. Can Romney win Ohio and perform decently in the conservative South? Will Santorum finally win a real primary, instead of only caucuses? Can Gingrich do well outside of Georgia? Romney's performance is particularly key, says CNN's Hamby. The South is "the GOP's most reliable voting bloc in general elections," and Republicans are worried Romney can't carry the region against Obama. "Tuesday could either squelch some of those concerns or exacerbate them." 

Sources: AP, Boston Globe, CNN, Los Angeles Times, Nooga, NPR, Politico, Washington Post (2), Wikipedia