It seems like a hundred polls are released every day now that the Iowa caucuses are less than a month away. Here's our guide to which ones matter and why.

Findings: In Iowa, Newt Gingrich at 22 percent, Ron Paul at 21 percent, Mitt Romney at 16 percent, 
Pollster: Public Policy Polling
Methodology: 555 likely Republican caucus goers, polled from December 11 through 13 through automated telephone interviews.
Why it matters: Gingrich, though still ahead, is losing strength in Iowa. PPP found his lead dropped from 9 percentage points to just one. And the poll doesn't appear to be an outlier, as it follows two other polls with similar findings. A University of Iowa poll released Monday found that once Herman Cain dropped out of the race, Gingrich's support slipped from 37.7 percent to 24.4 percent. Plus Gingrich's lead is smaller among "very likely" caucus-goers as well as "strong Republicans." American Research Group also found Gingrich leading by a smaller margin -- his support shrank from 27 percent in the poll released November 23 to 22 percent in the one released Monday. (Romney also dropped, from 20 percent to 17 percent.) 
Caveat: PPP leans liberal, though though it has a pretty good record of being accurate. PPP also asks funny questions that some say could lead to less-than-serious responses. Example: Would Obama be raptured in the Apocalypse?

Findings: Mitt Romney beats President Obama 48 percent to 43 percent in 12 swing states. Obama loses to Newt Gingrich, too, 45 percent to 48 percent.
Pollster: USA Today/ Gallup
Methodology: 1,132 registered voters polled from November 30 through December 7.
Why it matters: Obama, obviously, needs to win at least some of these states -- Colorado, Florida, Iowa, Michigan, Nevada, New HampshireNew MexicoNorth Carolina, Ohio, Pennsylvania, Virginia, Wisconsin -- to get reelected. And he's been trying to reach out to voters there -- he's visited swing states more than any other previous president and gives frequent interviews to local news stations. So far, it's not working, or at least not enough. A majority in these states don't think they're better off now than they were three years ago, though a majority of young people do. The number of registered Democrats has shrunken by 4 points while the number of Republicans has grown by 5 -- and how many people you have on your side matters a lot in close elections where you need to turn out as many of your voters as possible.
Caveat: NBC News' First Read notes, "It’s striking to see this kind of discrepancy between the swing-state and nationwide numbers. So a bit of caution..."

Findings: In New Hampshire, Romney is first with 33 percent, Gingrich is in second at 22 percent, and Ron Paul's in third with 18 percent. 
Pollster: Rasmussen
Methodology: 721 likely Republican primary voters in New Hampshire on December 12.
Why it matters: All year, the conventional wisdom has been that Paul's support has a ceiling of 15 percent or so. But Paul has been running a ton of negative ads against Gingrich, and they might be working. Paul is catching up third Gingrich for third place in New Hampshire, having cut the space between them from 10 points to 4 points. and with Romney for second place in Iowa. And Paul is gaining on Gingrich in Iowa -- two polls put him in second or tied for second. Both Public Policy Polling and Rasmussen find Paul really strong among young voters. 
Caveat: Rasmussen doesn't have a perfect track record.