The Republican presidential debate from the Ronald Reagan library in Southern California will be voters' first chance to see the current frontrunner for the GOP nomination, Texas Gov. Rick Perry, on the same stage with Mitt Romney, the previous pack leader.
Yes, there will be other candidates on the stage, all of whom have their various supporters who still believe, more or less.
But it takes a prodigious imagination to see a clear path to the nomination for the two current members of Congress now in the field, Ron Paul and Michele Bachmann.
The same holds for Jon Huntsman, the former Utah governor; Newt Gingrich, the former House speaker; Herman Cain, the former head of Godfather's Pizza, and Rick Santorum, the former U.S. senator from Pennsylvania.
Which gets us back to Perry and Romney who, for different reasons, are likely to be tested in the debate that will be carried on MSNBC at 8 pm ET.
For one, they will be questioned by NBC News anchor Brian Williams and Politico editor John Harris, two journeymen journalists who have their organizations' and their own serious reputations to uphold.
That means that to maintain their journalistic street cred, Williams and Harris need to be at least as pointed in their questioning as Fox News Channel's team during the previous GOP presidential debate, an effort for which FNC was widely praised.
Both Perry and Romney present target-rich candidacies for the journalists so it shouldn't be hard to test the candidates.
Perry, for instance, will likely be questioned about any number of the assertions in his book Fed Up! Our Fight To Save America From Washington which play well to a certain segment of the Republican base but not more broadly.
For example, how can he expect to be a viable general election candidate after calling Social Security a "Ponzi scheme" and a "failure?"
As no less a political strategist as Karl Rove noted Wednesday on ABC's Good Morning America, those views are "toxic" even within the GOP primary electorate, let alone general-election voters.
True, there's no love lost between Rove and Perry. But that doesn't diminish the fact that Perry is going to have to answer difficult questions on Social Security among issues.
Like his apparent nostalgia for the time when senators were chosen by state officials and not popularly elected.
And the inconvenient questions won't only come for the journalists, they're likely to come from the other candidates on the stage, too.
Romney, for instance, has the challenge of trying to knock Perry down a few pegs. What better way to do it than to go after Perry as extreme and intimate that the Texan's views will make it more difficult for him to beat President Obama?
But Romney has his political Achilles heels, too, which Williams and Harris, the journalistic questioners, Perry and the other candidates are likely to go after as well.
Romney, for instance, has made the center of his campaign the notion that his history as a successful businessman demonstrates that he knows how to create jobs.
But as came up in the last candidates' debate, when he headed Bain, the private equity firm, he oversaw layoffs of American workers. Romney was able to quickly change the subject in the last debate; he probably won't be able to do it as easily tonight.
Also, Romney's job creation record as Massachusetts governor in the mid-2000s has been questioned, with critics, including Huntsman, skewering him for the Bay State's rank of 47th in job creation when Romney was chief executive.
While the race for the Republican nomination appears now to be between Perry and Romney, Bachmann, Paul, Santorum, Gingrich, Huntsman and Cain will do everything they can to keep the guttering flames of their campaigns burning. That will most likely take the form of potshots at Perry and Romney.
But they aren't the main event. Texas' current governor and Massachusetts' the former one are.