As we close out 2013, here's a look at the senators at risk of losing their primaries. It's worth noting that it's a relatively rare event for senators to fall in a primary—in 2012, only former Sen. Richard Lugar, R-Ind., lost to a primary challenger, and the previous cycle just Sens. Robert Bennet, R-Utah, and Lisa Murkowski, R-Alaska, did—though Murkowski came back and won reelection as a write-in candidate. So, keeping in mind that we predicted in our final Hotline Spotlight of the year that no Senate incumbent will lose a primary next year, here are the candidates who should...