Presidential politics, like nature, abhors a vacuum — as evidenced by the constant ebb and flow at the top of the GOP race for the White House.

And nothing creates a vacuum like a serious contender dropping out of the race.

In light of some flops on foreign policies issues, as well as multiple accusations of inappropriate conduct and a new allegation of a protracted extramarital affair, Georgia businessman Herman Cain said Tuesday he is "reassessing" his campaign.

This, of course, is leading to wide speculation that the end of his run may be imminent. So we asked South Carolina political experts to speculate on who stands to benefit the most from Cain's potential departure.

At the top of the list Newt Gingrich, former Speaker of the House, who stands to continue his dominance at the top of the latest polls with Cain's fall.

"As the allegations against Cain mount and he continues to fall in the polls, Newt Gingrich is in the best position to capitalize," said Robert Oldendick, political science professor at the University of South Carolina in Columbia. 

"Gingrich has performed well in recent debates and his campaign has seemed to become more organized and more focus. His endorsement over the week-end by the Manchester Union-Leader has generated some positive coverage and he is emerging as the conservative alternative to a Romney nomination."

Gingrich's rise — from 3 percent in July to 33 percent in November, according to the American Research Group — has coincided strongly with Cain's dip. According to ARG's polling of likely voters over Thanksgiving weekend, Cain's numbers plummeted from 26 percent in October to 10 percent in November.

But there are some who speculate that Gingrich's reputation as an establishment Republican may temper expectations of siphoning off former Cain support.

"Herman Cain is such an unusual candidate," said Danielle Vinson, political science chair at Furman University.  "Some of the folks he's been pulling support from are interested in him because he's an outsider. And Gingrich is not an outsider.

"I imagine at least some of the folks who had been rooting for Cain because he's not Romney will go to Gingrich. Some of the ones who were liking his outsider status may find themselves leaning toward Bachmann or (Rep.) Ron Paul, or even (Gov.) Rick Perry."

Oldendick also mentioned Perry as a possible beneficiary from Cain's fall.
 
"Rick Perry will also benefit some from Cain’s drop in popularity, in that they appeal to many of the same voters. Perry appears to be regaining some of his footing after some stumbles in the debates, and has enough money to compete strongly, at least through South Carolina," Oldendick said.

"Ron Paul will also attract a few of Cain’s supporters — those that are most opposed to 'mainstream' candidates and like Cain’s 'outsider” image."

There are also remain serious questions regarding Gingrich's own personal baggage and history of marital infidelity. Such issues are almost certain to lead to increased scrutiny, Vinson said.

"You're seeing it already in terms of polls I've seen, that Gingrich is not doing as well among women — at least not in South Carolina he's not. Some people have forgotten about a lot of what they knew about him when he was Speaker," Vinson said.

"I imagine as scrutiny turns on him now and his poll numbers take off, people will remember those things. Those personal issues will come back."

Still, Oldendick said, it stands to reason that Gingrich's powerful position as the most conservative alternative to Romney would only be bolstered by the departure of a former frontrunner.

"Overall, it appears that Gingrich will benefit the most from Cain’s decline," he said.