Another Iowa poll shows tight presidential race, single-digit lead for Chuck Grassley over Patty Judge

In more support for forecasters who view Iowa as a toss-up state, Donald Trump leads Hillary Clinton by a statistically insignificant 40 percent to 39 percent in a new CBS News Battleground Tracker Iowa poll conducted by YouGov. About 3 percent of the 998 “likely voters” surveyed between July 13 and 15 back Libertarian Gary Johnson, 2 percent Green Party candidate Jill Stein, 7 percent “someone else” and 8 percent are “not sure.”

Among respondents supporting Clinton, 50 percent said it is mainly because they like her, 37 percent said mainly to oppose Trump, and 13 percent said mainly because she will be their party’s nominee. The opposite was true for respondents planning to vote for Trump: 53 percent said they will do so mainly to oppose Clinton, 36 percent said mainly to support Trump, and 11 percent said because Trump will be their party’s nominee.

In Iowa’s U.S. Senate race, the CBS/YouGov poll found Senator Chuck Grassley ahead of Democratic challenger Patty Judge by 45 percent to 37 percent, with 16 percent not sure and 2 percent favoring “someone else.” In his previous re-election bids, Grassley has never been below 50 percent and less than 10 points ahead of his challenger in any public survey by a reputable pollster. YouGov now becomes the third firm (after Public Policy Polling and Loras College) to find a single-digit lead for the incumbent.

The full questionnaire for the CBS/YouGov poll is available here, along with cross-tabs. Assuming random sampling techniques produced a representative respondent pool, the margin of error for this survey would be plus or minus 4.8 percent. One possible problem with the sample: 41 percent of respondents said they are currently registered Republicans, 42 percent registered Democrats, and just 14 percent “not affiliated with either party.” More than 31 percent of Iowans who cast ballots in the 2012 general election were no-party voters. It’s possible that many of the registered Republicans or Democrats sampled by YouGov think of themselves as “independents” but changed their registration in order to participate in the February 1 Iowa caucuses or June 7 primaries.

YouGov polls are conducted over the internet; the firm received a “B” grade in FiveThirtyEight’s pollster ratings.

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