Sen. Chuck Grassley (R-Iowa) faces a still-healthy but declining popularity among Iowa voters amidst his high-profile role in the national debate over healthcare.

57 percent of Iowa voters approve of the way Grassley, who will stand for reelection next fall, is handling his job. 33 percent disapprove, while 12 percent are unsure of their feelings toward the veteran senator.

While Grassley remains well above the 50 percent threshold considered healthy for incumbents, his popularity has dipped from a high of 75 percent in January, according to a new Selzer & Co. poll of Iowa voters, commissioned by the Des Moines Register.

Grassley has been the lead Republican negotiator in negotiations over a bipartisan healthcare bill as ranking member of the Senate Finance Committee.

That position has bolstered his standing among Iowa Republicans, the poll found, but taken a toll among independent voters, and an even larger one among Iowa Democrats.

Grassley's approval rating has spiked 10 points among GOP voters, put fallen 11 percent among independents, and gone down 24 percent among Democrats.

45 percent of Iowa voters said they would definitely support Grassley's reelection next year, a fairly strong starting point for the Iowa Republican. 24 percent of Iowa voters said they would consider an alternative, while 13 percent would definitely vote for another candidate. 11 percent said they would not vote, while seven percent were unsure.

The poll, conducted September 14-16, has a 3.5 percent margin of error.