(NBC) -- Join is tonight for a special edition of Rock Center with Brian Williams as Brian, the National Journal's Beth Reinhard and the Tampa Bay Times' Adam Smith moderate the first weekday primetime airing of a primary debate on a broadcast network of the 2012 presidential campaign.

All four qualifying Republican presidential candidates will attend tonight's debate on the campus of the University of South Florida in Tampa Bay.  The two hour special starts at 9 p.m. Eastern (8 p.m. Central).

When the remaining four presidential candidates gather for the 18th debate of the cycle tonight in Tampa, FL, the stakes couldn't be any higher, especially for Mitt Romney and Newt Gingrich.

For Romney -- fresh off his double-digit defeat in South Carolina and after uneven performances in his last two debates -- tonight's debate is a crucial moment for his campaign. Either he rises to the occasion (by providing sharper answers, by disqualifying Gingrich, and by proving to GOP voters the confidence he can be their guy in November), or he struggles again, giving Gingrich a path to overtake him in Florida.

For Gingrich, tonight's debate will prove if he can withstand the attacks (because they're coming), and if he can pull off another strong performance. And don't lose sight of Rick Santorum (who has leveled pointed criticism at both Romney and Gingrich in past debates) or Ron Paul (who has sometimes has served as Romney's wingman).

If we learned anything from South Carolina, it's that the debates have mattered, and tonight's debate likely won't be any different. By the way, this is the first debate where, based on actual results, it's clear there's no real front-runner right now.