Democrats have two prominent Senate primaries coming up on Tuesday, May 18, in which incumbent senators face challenges from the left.
In Arkansas, Sen. Blanche Lincoln is leading Lt. Gov. Bill Halter by double digits in polls, as unions and progressive groups have spent millions to support Halter's bid.
In Pennsylvania, Sen. Arlen Specter--who gave Democrats their short-lived 60-seat Senate majority just 13 months ago--has the support of the DC Democratic establishment as he faces a challenge from Rep. Joe Sestak that's too close to call according to surveys released this week.
Here's the latest polling on those two races, from Pollster.com: