Newt Gingrich's political carrer was brought back from the dead in May, killed in June, resurrected again in November, killed again in January, and reanimated again Thursday, according to three of the six new polls of the South Carolina primary. Here's our guide to today's polls and why they matter.

Findings: Gingrich is ahead of Romney in the South Carolina primary, which is just a couple days away.

Pollster: Public Policy Polling, Rasmussen, Insider Advantage

Methodology: Survey of 379 likely Republican voters; survey of 750 likely Republican voters; survey of 718 registered voters who say they'll vote Saturday. All three of these polls were taken January 18 and used robo-calls. 

Why it matters: It was considered a huge achievement for Mitt Romney when he pulled ahead of Newt Gingrich in South Carolina after the Iowa caucuses. Gingrich had been the frontrunner in the state since Thanksgiving, and before him, Herman Cain, and before him, Rick Perry. South Carolina evangelicals were expected to be hostile to Romney for his Mormon faith and moderate record, but after Iowa, there was talk that Romney could pull off a hat trick, winning the first three early voting states. On Thursday, that dream faded, as the Iowa Republican Party announced Rick Santorum won the caucuses after all, and new polls were released. Gingrich won a lot of praise with his performance in Monday's debate, but until today, it wasn't clear that his one-liners would translate to voters support. Now the evidence is piling up. PPP has Gingrich with 34 percent, Romney with 28 percent. Rasmussen has Gingrich with 33 percent; Romney with 31 percent. Insider Advantage has Gingrich with 32 percent, Romney with 29 percent. 

The New York Times' Nate Silver says that Gingrich has a lot of momentum, and has changed his forecast to give Gingrich and Romney equal chances of winning the South Carolina primary. Romney doesn't appear to have lost votes, Silver writes, but Gingrich has gained them from undecided voters and former Rick Perry and Rick Santorum fans.

Public Policy Polling offers some evidence to support speculation about where that momentum comes from. The Democratic pollster found that 56 percent of voters said they watched Monday's debate, and debate watchers favor Gingrich 43 percent to Romney's 27 percent. Among those who didn't watch the debate, Romney is ahead by 6 percentage points.

Caveat: Two polls -- from NBC News/ Marist and Politico/ Tarrance Group -- with live interviews show Romney still ahead. NBC puts Romney up 34 percent to Gingrich's 24 percent, while Politico says Romney is ahead 37 percent to Gingrich's 30 percent. Both did some of their polling before Monday's debate. Notably, the NBC poll found Romney's lead to be shrinking after the debate, while the Politico poll found Gingrich is the most popular second choice.

Talking Points Memo has a nifty little graph of how the race has changed in South Carolina: