About 57 percent of likely Iowa Republican primary voters support Terry Branstad, according to a new poll by Selzer and Co. for The Des Moines Register. Just 29 percent plan to vote for Bob Vander Plaats, and 8 percent plan to vote for Rod Roberts. The Des Moines Register poll surveyed 1,793 Iowans at least 18 years old, and the sub-sample of Republican primary voters included 501 people. (That included independents who said they planned to vote in the GOP primary; Iowa allows people to change their party registration on primary election day.) The poll was in the field from June 1 through June 3, and results for the likely Republican voters have a margin of error of plus or minus 4.4 percent.

Two other recent Iowa polls by Public Policy Polling and Research 2000 for KCCI have found Branstad comfortably ahead of Vander Plaats and Roberts but below 50 percent. In the 2002 Republican primary, Vander Plaats did much better than his final poll numbers, but he benefited that year from a highly negative campaign between Steve Sukup and Doug Gross.

This primary might have played out differently had Vander Plaats had more resources to make his case. About 34 percent of likely Republican primary voters weren’t sure whether they had a favorable or unfavorable opinion of Vander Plaats, and 60 percent said the same about Roberts. Branstad not only is much better known, he also scored highest on attributes like “best ideas for bringing new jobs to Iowa” and “best able to curb government spending” (which is laughable when you consider Branstad’s record on fiscal issues).

I will never understand why the Club for Growth and other national right-wing organizations decided not to get involved in the Iowa governor’s race. Given the way the national conservative movement pushed Marco Rubio against Florida Governor Charlie Crist, you’d think they would have some issues with Branstad (who received a “D” grade from the Cato Institute when he was governor).

Selzer’s poll for the Des Moines Register also asked likely Republican primary voters several questions about gay marriage. While 77 percent of them agreed that “Iowans should have a chance to vote on changing the constitution to specifically ban gay marriage,” I was surprised to see that 20 percent of likely Republican voters disagreed with that statement.

Meanwhile, only 50 percent of likely GOP primary voters agreed that “Iowans should vote to remove current Supreme Court justices from their office because of their decision on gay marriage.” An amazing (to me) 45 percent disagreed with that statement. Regarding the statement, “Some Iowans have overreacted to this issue, and having gay marriage in Iowa is just not that big a deal,” 35 percent of likely Republican primary voters agreed, while 62 percent disagreed.

Share any thoughts about the Des Moines Register’s poll in this thread.