Gingrich’s debate challenge: Keep pressure on Romney

Down another contender in the race for the Republican presidential nomination, the four remaining candidates will square off Thursday night for the last time before the South Carolina primary.

The two-hour CNN-sponsored debate at the North Charleston Coliseum will start at 8 p.m. Eastern time, capping off a tumultuous day that began with Texas Gov. Rick Perry’s abrupt exit from the race. He is the second contender in less than a week to drop out. Former Utah Gov. Jon Huntsman Jr. quit on Monday.

For Perry’s supporters -- few as they may be -- the debate may help decide who to back instead. Perry had been polling in the low single digits here, but with Mitt Romney and Newt Gingrich nearly tied, according to a Real Clear Politics average of recent polls, even a percentage point or two could make the difference when voters go to the polls Saturday.

If Romney’s seemingly inevitable march toward the nomination is to be stopped, Gingrich appears best positioned to do it.

Romney is at his most vulnerable point now, a fact that Gingrich well knows. And momentum seems to be on Gingrich’s side.

Polls show Gingrich surging, and Perry threw his support behind the former House speaker on Thursday. Meanwhile, certified results from the Iowa caucuses declared Rick Santorum the actual winner there, stripping Romney of his claim to have won the first two nominating contests of the year.

Gingrich got a bump in the polls after an aggressive performance in a debate on Monday. Watch for him to double down on that strategy Thursday night, aiming mostly at Romney.

But Gingrich has a serious problem, one that could overshadow any gains he makes on the debate stage. ABC News will air an interview Thursday night with Gingrich’s second wife, who claims that Gingrich asked her for an “open marriage,” a charge that could send many of his social conservative backers looking elsewhere.

With Perry out, there’s only one place left to look: Santorum.

Santorum may have won the Iowa caucuses – a victory that will be forever clouded by the disappearance of ballots from eight precincts – but he’s trailing here, battling Ron Paul for third or fourth place.

A fourth-place finish would make it hard for Santorum to justify staying in the race, especially if Gingrich wins or places close second. Santorum’s best bet is to get through the debate without making any mistakes and let Romney and Gingrich beat each other up.

There’s not much on the line for Paul. He and his loyal backers care less about party unity than about promoting his libertarian agenda, so this primary is not a make-or-break moment for him. Still, he has benefited up until now from a large field that has prevented consolidation around Romney and a not-Romney alternative. When -- or if -- that happens, Paul’s candidacy will become less relevant, as will his presence at the debates.