The Republican presidential debate marathon continues tonight in Orlando, Florida where nine candidates will gather to talk politics for the third time in 15 days.

The proceedings start at 9 p.m. — way too late but no one asked the Fix’s opinion — and will be carried live on Fox News Channel.

We’ll be live-blogging the proceedings in this space using a different format than we normally do. Those of you who are accustomed to following the debates with us in Cover It Live will be able to participate on Twitter by sharing your observations using #DebateTheFix.

But before we get to that, we thought it was worth giving Fixistas a cheat sheet of the major storylines to keep an eye on tonight. You can also scroll to the bottom of this post to see what people are saying on Twitter about the debate.

Have thoughts of your own on what to watch for? The comments section awaits.

* Perry proving ground: The Texas governor has been only ok — and that’s being charitable — in his first two debates, a decidedly uneven set of performances that have given some within the GOP establishment pause about jumping on board with him but have done little to effect his frontrunner status in the race. A third weaker-than-expected performance tonight, however, could cement the idea that Perry is something less than advertised and could well lead to a re-examination of whether the title of “frontrunner” really fits him.

What Perry has going for him is that Republicans — from the activist community all the way up to major donors — seem to want him to succeed. They are looking for any sign, literally, that he is ready for primetime and would be comfortable sharing a stage with President Obama next fall. This is Perry’s best chance to clear that relatively low bar.

(One potential warning sign: Perry and his team insist they are doing nothing different to prepare for this debate than what they did for the first two gatherings. People looking for Perry to deliver a break-out performance need to hope that’s just spin.)

* How hard will Mitt hit (and where)?: Romney made clear in the last Florida debate — 10 days ago in Tampa — that he was ready and willing to go after Perry on Social Security, asking if the governor truly believed it was unconstitutional. What Romney was — and is — trying to do is use Social Security as a stand-in for electability, doing everything he can to seed doubts in the minds of Republican voters about whether Perry could really beat Obama.

The problem with Romney seizing on Social Security as the main point of attack against Perry is that in so doing he is positioning himself to the ideological left of many Republican primary voters. In a Quinnipiac University poll in Florida out this morning, 52 percent of Republicans agreed with the idea that Social Security is, as Perry has repeatedly called it, a “Ponzi scheme”. (Six in ten Republicans also said Perry wants to “fix” Social Security while 14 percent said he wants to “end” it.)

What Romney then needs to do tonight is use Social Security as a gateway into more red-meat conservative issues that raise further electability questions about Perry.

* Two Faces -- Bachmann and Huntsman: Minnesota Rep. Michele Bachmann and former Utah governor Jon Huntsman have each been quite good and decidedly bad at different times during the handful of presidential debates so far this year.

Bachmann has shown a capacity to channel the fighting spirit and anti-Obama sentiments that the Republican base loves. (Her performance in the June New Hampshire debate was an absolute gem.) She has also shown an ability to disappear into the background, leaving no impression and looking decidedly like a second tier candidate. (See the California NBC/Politico debate.)

Huntsman has had the same issue. After putting together a very solid performance on Sept. 7 in California, Huntsman delivered one of the most baffling debate performances we can recall five days later in Florida. (Nirvana reference!)

Who comes on stage tonight will matter for the general tone and tenor of the proceedings. Bachmann scored a direct hit on Perry over his HPV vaccine decision in the Florida debate ten days ago (and then proceeded to step on that momentum with her “mental retardation” comment) and got him off his game. Huntsman, when he is good, can be the sort of big picture leader that many in the Republican establishment covet.

When Bachmann and Huntsman are bad, well, they are really bad. Who will show up tonight?

* Foreign policy front and center: With President Obama speaking at the United Nations and Perry issuing a blistering critique of the the Administration’s Middle East policy already this week, it seems likely that foreign policy, which has been almost entirely nonexistent in past debates, will play a larger role in this one.

Former Pennsylvania senator Rick Santorum has already signaled that if the Middle East comes up, he is ready and willing to go after Perry on the subject. “I’ve forgotten more about Israel than Rick Perry knows about Israel,” Santorum said earlier this week in an interview with Politico. And look for former House Speaker Newt Gingrich to try to flex his mental muscle if foreign policy becomes a major point of discussion tonight too.

Given the dominance of the economy on voters’ mind, foreign policy chops aren’t going to win the nomination for Perry or anyone else. But, an ability to speak fluently about the various hot spots around the world does go to the central question that these debates and Republican voters are trying to answer: Which candidate is best equipped to beat President Obama next November?

* The Johnson factor: For the first time in more than four months, former New Mexico Gov. Gary Johnson will join the eight usual suspects in a debate.

What will it mean? Absolutely nothing.

Here’s a look at what people are saying on Twitter about tonight’s Florida Republican debate.