Tonight's GOP presidential debate in Sioux City, Iowa is technically the 13th time most of the candidates will appear on stage to discuss the issues and defend their records. But this final debate before the first in the nation caucuses is not only the last; it's the one that probably matters most. The latest poll of likely Iowa Caucus participants shows that former Massachusetts Governor Mitt Romney is holding a tiny lead over his nearest competitor, but he's been at or near that position throughout the seemingly endless string of debates while the anti-Romney crowd has migrated to a different challenger each month. Tonight's performances could determine whether that crowd of mostly conservative Iowans will finally settle on one of the other contenders or settle for Governor Romney.

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After five years of campaigning for this job, Governor Romney has finally stopped avoiding the media (he has given nearly as many interviews this week as he has since declaring his 2012 candidacy in June). He has also finally taken some hits in the most recent debates. While his support remains in the low-20's, he hasn't been able to close the deal with the conservative majority of Iowa's Republicans and with his day-to-day focus obviously on New Hampshire, tonight is probably his last chance to make the sale in the Hawkeye State.

Former Speaker of the House Newt Gingrich recently took his turn at the top of the leader board with his new stay-positive, grandfatherly persona and undisputed debating skills. But reminders of his past personal indiscretions, sometimes liberal positions and the $1.6 million he earned as a consultant to government-backed Freddie Mac have cost Mr. Gingrich at least a few points in the polls. And he didn't do his cause any favors recently when after an attack by Governor Romney over that $1.6 million, Mr. Gingrich lashed out against Mr. Romney's success in the private sector saying, "If Gov. Romney would like to give back all the money he's earned from bankrupting companies and laying off employees over his years at Bain that I would be glad to then listen to him." That kind of anti-capitalist rhetoric in defense of government-funded "consulting fees" definitely raised some conservative eyebrows and demonstrated how, when attacked, Mr. Gingrich has a tendency to grab for any weapon to defend his political career even at the expense of his alleged conservative ideals. This leaves us wondering if it will be the stay-positive grandfather or the impulsive, erratic Newt of old that shows up tonight.

Congressman Ron Paul (R-Texas) will undoubtedly hold onto his core supporters no matter what he says in tonight's debate. But will he be able to sell his less than mainstream ideas to the conservative Republicans he'll need to win in Iowa? Representative Paul has been able to capture the imagination of some of the anti-Romney folks who limped away from the Cain Train Wreck. But can he defend his non-intervention positions in both foreign and social policy enough to win their votes? Or will his performance tonight inspire more of those comparisons to the crazy uncle at Thanksgiving dinner?

Those who have been tuning into the debates to see another "oops moment" from Texas Governor Rick Perry have been very disappointed of late. After serious stumbles in his first few performances, the candidate who readily admits he's not the best debater has exceeded expectations in the last few contests. The big question for him tonight is will he continue this upward trend? If he can effectively highlight his jobs record in Texas, his Christian values and his strong belief in "American exceptionalism" he may be able to influence the nearly two-thirds of Iowa caucus goers who say their minds can still be changed.

Even the candidates currently with single digit levels of support could make a major move with a stellar performance in tonight's debate. With the caucuses less than three weeks away and the debate televised on the very popular Fox News Channel; Congresswoman Michele Bachmann (R-Minnesota), former Utah Governor Jon Huntsman and former Senator Rick Santorum will get the chance to shine in front of what should be one of the largest and most attentive audiences yet.

History has shown that one memorable sound byte during one event held close to actual caucus or primary voting can change a candidate's fortunes. Who could forget Candidate Ronald Reagan's "I am paying for this microphone!" from the 1980 primary campaign? President Reagan later said of that moment, "I may have won the debate, the primary - and the nomination - right there."

There just might be a winning moment like that tonight.