Longtime Iowa Senator Chuck Grassley continues to outpace Democratic challenger Roxanne Conlin in his bid for a sixth term in the U.S. Senate.

A new Rasmussen Reports telephone survey of Likely Iowa Voters finds the Republican incumbent earning 55% of the vote. Conlin receives support from 37%. Three percent (3%) prefer some other candidate in the race, while five percent (5%) are still undecided. (To see survey question wording, click here.)

In surveys dating back to early February, Grassley has consistently held a double-digit lead over his Democratic opponent. In those surveys, Grassley's support has remained in the narrow range of 53% to 55%, while Conlin has picked up 35% to 40% of the vote. Last month, Grassley led Conlin 55% to 35%.