Forty-nine percent of likely Iowa voters said they would reelect the veteran GOP senator, compared to 40 percent who said they would support Roxanne Conlin, a Democratic attorney running against the senator.

Eleven percent of Iowans said they were undecided in such a match-up. Grassley has won reelection with 66 percent of the vote or more in each of his bids since first being elected in 1980 with almost 54 percent of the vote.

The poll puts Grassley beneath the 50 percent threshold that is considered healthy for incumbents running for reelection, though Grassley's favorable rating is somewhat higher: 58 percent of Iowans say they have a favorable view of the five-term senator, while 37 percent have an unfavorable impression.

During his almost three decades in the Senate, Grassley has risen to become the top Republican on a number of committees, serving currently as ranking member of the Senate Finance Committee, on which he spearheaded negotiations toward a bipartisan solution on healthcare.

But while some of Grassley's Senate GOP colleagues have faced an uprising in their Republican base back at home, 85 percent of Iowa Republicans say they'd support the incumbent senator over Conlin.

The Iowa Poll
, conducted by Research 2000 from May 3-5, has a 4 percent margin of error.