The Des Moines Register released more results from its latest Iowa poll by Selzer and Co., and Senator Chuck Grassley’s approval rating was 57 percent, the same as in the Register’s September poll. Only 32 percent of respondents said they disapproved of Grassley’s work.

Grassley’s 57 percent approval figure remains well short of the 75 percent he began the year with. […]

Political independents and Democrats have been responsible for much of Grassley’s slide since January. He made up little ground with them this fall. […]

More than half of Republicans say he did an excellent or good job on health care, while only about a quarter of Democrats and 39 percent of independents rate his work positively.

In a head to head matchup against Roxanne Conlin, Grassley led 57 percent to 30 percent. Last month’s Research 2000 poll of Iowans found Grassley leading Conlin by a much narrower margin, 51 percent to 39 percent. I’d like to see more polling of this race, but given Selzer’s track record in Iowa, I’m going to assume that the Register poll is close to the mark.

Since the media won’t be as focused on health care reform in the autumn of 2010, Democrats will need to build a case against Grassley that goes beyond his double-dealing on that issue. Even if Democrats run a near-perfect campaign against Grassley, he is very likely to be re-elected unless he makes some unforced errors.

On the other hand, it’s worth remembering that Grassley’s never been re-elected with less than 66 percent of the vote before. Holding him below 60 percent, or better yet below 55 percent, would greatly help down-ticket Democratic candidates next November.

Incidentally, Selzer’s poll for the Register found Senator Tom Harkin’s approve/disapprove numbers at 54/33, which is fairly strong but down from the 70 percent approval rating Harkin had in the Register’s January poll.