With at least one lifelong National Rifle Association member -- Sen. Joe Manchin (D-W.V.a) -- jumping on board with pushing new gun control measures in the aftermath of the tragedy in Newtown, Conn., we thought it worthwhile to look at where the other senators stand.

Guns are a very regional issue that often don't fall neatly along party lines. There are many Democrats who have great ratings from the NRA, and some Republicans who have not-so-good ratings.

Below, we look at the NRA and Gun Owners of America ratings for all 100 members of the new Senate in 2013 (and feel free to play with the data here). After the chart, a few takeaways.

1. If gun control gets done, a significant number of NRA allies will likely buck the group's wishes. Exactly half of the Senate has at least an 'A-' grade from the NRA.

2. The pivotal votes will be pro-gun Democrats like Manchin and Sen. Mark Warner (D-Va.), an 'A'-rated senator who has also called for a conversation on new gun laws. Other 'A'-rated Democrats include Sens. Max Baucus (D-Mont.), Bob Casey (D-Pa.), Tim Johnson (D-S.D.), Mark Begich (D-Alaska) and Jon Tester (D-Mont.) and Sens.-elect Martin Heinrich (D-N.M.) and Joe Donnelly (D-Ind.).

On the GOP side, the most likely proponent would seem to be Sen. Mark Kirk (R-Ill.) -- the only Republican who gets 'F' ratings from gun groups -- and Sens. Susan Collins (R-Maine), John McCain (R-Ariz.) and Dan Coats (R-Ind.), who haven't exactly been tight with the NRA.

3. Starting next month, more than half the Senate will have served one term or less. And because gun issues haven't really come up very often in recent years, many of those members have yet to build substantial voting records. That suggests there could be some surprises.