Eight Republicans candidates will take the stage tonight in New Hampshire for the seventh debate of the GOP nomination fight. But, the dynamics of this debate, which is being sponsored by the Washington Post and Bloomberg News will be different for several reasons.

(The eight men and women who will appear at the Dartmouth College Republican presidential debate in New Hampshire tonight.)

Second, businessman Herman Cain has gone from an afterthought (at best) in past debates to a centerpiece of this set-to. How Cain handles himself and how former Massachusetts governor Mitt Romney and Texas Gov. Rick Perry approach him will be a fascinating — and new — storyline.

We’ll be liveblogging every minute of the debate starting at 7:30 (or so) p.m. tonight. You can watch it all via a live video stream on washingtonpost.com and follow along right here too. (It’s all very tech-savvy and 21st century.)

But before we get to the main event, what better way to fiddle away the hours then to check out our look at what to watch for in tonight’s debate. Read it. Then use it to impress your friends and vanquish your enemies.

* Rick Perry at the center (sort of): The Texas governor desperately needs a strong debate performance to make people forget about how bad he has been in previous gatherings. (In case you forgot, Fix Rachel helpfully reminds you of Perry’s greatest debate misses.)

But, he faces an odd dynamic in that Romney and Cain will be seated center-stage tonight — reflecting their current standing in national polls — and are likely to receive the bulk of the questions. In a way, that setup might work to Perry’s advantage as the spotlight won’t be shining directly on him — a change from past debates.

At the same time, Perry will have to fight for air time far more than in the previous three debates in which he has participated. And, unlike in opast debates, he has to find a way tonight to demonstrate to activists and donors that he belongs on the stage.

Fail tonight and it could be a long road back for Perry.

* Where does Cain aim?: Cain is the pivot point in tonight’s debate. Not only will he get lots more attention — from the moderators and his rivals — than he has in the past but where he chooses to aim his rhetorical fire will also matter.

The assumption going into tonight’s debate was that Cain would target Perry since he has gone after the Texas governor repeatedly over the past few weeks and and the two men are, in theory, competing for the same tea party support.

But, in a radio interview today, Cain made clear it would be Romney not Perry who he would focus his attacks on. “I’m going after Romney,” Cain said. “I’m not going after Perry. I don’t need to go after Perry.”

Whether Cain is feinting or genuinely telegraphing his strategy remains to be seen. But if he does make good on his promise and attack Romney, that will be a major helper for Perry in his attempt to stand out. Of course, if Cain turns his fire on Perry, it could spell trouble for the Texas governor.

* Romney’s wheelhouse: Romney has spent the entire campaign — and basically the entire time since he lost the 2008 presidential nomination — focused on the economy. He knows the issue both as a private businessman and as a governor (though he’s far more likely to focus on his private sector experience). And he’s proven over the last five debates that he is the best debater in this field of candidates.

So, an economically-themed debate should be the best of all worlds for Romney. Complicating that somewhat is the fact that he is now the frontrunner in the race (again) and, as such, will likely be on the receiving end of attacks from , well, everyone.

But Romney is familiar with the role of political pinata in debates and is an able deflector of attacks. He’ll also enter the debate with a burst of momentum courtesy of the endorsement of New Jersey Gov. Chris Christie . Look for Romney to shine tonight.

* Bachmann’s last stand: Some time between tonight’s debate and the one set for Oct. 18 in Las Vegas, the Minnesota Congresswoman has to find a spark of momentum or run the risk of petering out entirely before the end of the year.

The latest evidence of Bachmann’s struggles? A new NBC/Marist survey in Iowa that puts her at 10 percent, well behind Romney and Cain. In an attempt to show positive movement, Bachmann continues to shuffle staff around. But that actually makes her campaign look even more chaotic.

Without a stand-out debate performance sometime in the next week it’s VERY hard to imagine how she remains at all relevant in this presidential conversation. Bachmann knows she has to make something happen. But given that she will not be part of the central conversation in the debate, she will likely struggle to emerge.