Face the Nation: RNC chief Reince Priebus and ex-Obama spokesman Robert Gibbs

This Sunday's guests are the chairman of the Republican National Committee, Reince Priebus, and Robert Gibbs, the former White House press secretary who now serves as an Obama campaign adviser. Also, Politico's Mike Allen will join CBS News Chief White House Correspondent Norah O'Donnell, Congressional Correspondent Nancy Cordes and Political Director John Dickerson in our roundtable.

With one month to go, it's basically now a two-man race. Even as Herman Cain "reassesses" his campaign after a woman came forward this week alleging a long-term affair with the Atlanta businessman, the Cain Train has fallen from the top of the polls.

"Cain is now at 8 percent among likely Republican caucusgoers, The Des Moines Register's new Iowa Poll shows. That's down from 23 percent in late October," writes Jennifer Jacobs in today's Des Moines Register - previewing next month's first in the nation Iowa caucus.

So it's down to Mitt Romney and Newt Gingrich for the Republican presidential race, though Representative Ron Paul has shown strength in Iowa and Texas Governor Rick Perry is on the air there with a television ad poking fun at his own debate flubs.

But all eyes are now on Gingrich, the former speaker of the House, who has decided to keep his positive message going, reportedly telling his staff not to attack his top rival Romney. But the Speaker himself couldn't pass up an opportunity to set himself apart from the former Governor of Massachusetts.

"I'm not interested in distinguishing myself from Romney. I'm happy to be who I am. I think that distinguishes me from Romney. You know, I'll let you guys worry about that stuff. The only person I want to focus on is Barack Obama," said Gingrich in Iowa, alluding to a drumbeat of criticism against Romney for flip-flopping on various issues.

Romney though has welcomed the criticism, especially when it comes from the Democratic National Committee, as it did in a hard hitting television ad running sparsely in a few key states. The ad highlights a new website, MittvMitt.com, and hits Romney for being on both sides of major issues.

"I don't know what they are afraid of, they don't want to see me as the nominee, that's for sure," Romney said this week in Florida. "It shows they are awfully afraid of facing me in the general election... bring it on, we're ready for them," he said.

Democrats are all too eager to sling arrows at Romney, hoping to drive a wedge between the presumed front runner and conservative voters who have been long weary of Romney's conservative convictions.

The DNC website has a video highlighting Romney's various stances and answers its own question. "What does Romney believe? Whatever it takes to get elected," it says.

So why are Democrats so eager to attack Romney? Will they also attack Gingrich? Who benefits the most if Cain drops out of the race? Why haven't conservatives rallied around Romney, even though many Republicans say he's the party's best bet to beat President Obama? What can Romney do to convince them to back him? With the economy sluggishly rebounding, can Obama win a second term? What can the President do to convince voters he deserves a second term as unemployment lingers above 8 percent?

Those will be among the issues discussed as Reince Priebus, the chairman of the Republican National Committee and Obama campaign adviser Robert Gibbs join Bob Schieffer to Face the Nation.