The failure of an amendment offered by Sens. Joe Manchin (D-W.Va.) and Pat Toomey (R-Pa.) to expand background checks effectively doomed President Obama's efforts to reform gun laws following the massacre in Newtown, Conn., in late 2012.

We've written a fair amount about the vote (and why it failed) but everything you really need to understand about it is contained in this chart put together by the Sunlight Foundation. They plotted the number of gun businesses in the states of a handful of key senators and the percentage of the vote President Obama won in those same states in 2012.

Based on those two factors, they concluded -- way back in early February! -- that Sens. Max Baucus (Mont.), Mark Begich (Alaska), Tim Johnson (S.D.) and Mark Pryor (Ark.) were the four Democrats most likely to vote against a gun control measure. (The quartet had the highest number of gun businesses and the lowest Obama percentages.)

Bingo. They were right on all but Johnson -- and his yes vote on Manchin-Toomey has more than a little to do with the fact that he isn't seeking re-election in 2014.

What's clear is that based on this simple calculation -- gun businesses in state + Obama percentage (with a little when you are up for reelection thrown in) -- anyone could have surmised months ago how any vote on a gun control measure would ultimately play out.

The full chart is below.