Competitive primaries helped Iowa Republicans make “significant” voter registration gains between June 1 and July 1 of this year, Iowa Secretary of State Michael Mauro announced at a press conference today. Voter registration totals as of June 1 (pdf file) were 710,017 Democrats, 607,567 Republicans and 772,725 no-party voters. As of July 1, registered Democrats were down to 699,972, Republicans were up to 644,838, and no-party voters were down to 749,441. A press release from the Secretary of State’s office noted that “these totals include both active and inactive voters.”

Iowa law allows voters to change their registration on the day of a primary or general election, and there were many more competitive races on the Republican side this year. It appears that approximately 10,000 Democrats and 23,000 independents became Republicans in order to vote in the GOP primary on June 8. Mauro remarked that Republicans gained in voter registration in 2002, when three men sought the nomination for governor and two sought the nomination for U.S. Senate. By the same token, the number of registered Democrats increased substantially in 2006, when Chet Culver was running against Mike Blouin and Ed Fallon while Jim Nussle was unopposed for governor on the GOP side. But Mauro “couldn’t deny that the momentum is on the GOP side.”

Not every party-switcher is a guaranteed Republican vote in November. Some Democrats may have voted for the perceived weaker Republican candidate for governor, and I’ve known independents who vote in whatever primary is competitive, no matter whom they plan to support in the general. Nevertheless, it’s not good for the Iowa Democratic Party’s voter registration advantage to shrink by such a large amount, particularly since it will be challenging to turn out many of 2008’s new voters, who were mobilized by Barack Obama’s campaign. Approximately 1.5 million Iowans voted in November 2008, but only about 1.05 million voted in November 2006. I will be surprised if turnout this November exceeds 1.1 million.

Click here for updated voter registration numbers by county and by Congressional, state house and state senate districts. After the jump I’ve posted links to pdf files showing voter registration changes following the 2002, 2006 and 2010 Iowa primaries.

Iowa Democrats’ ability to execute their early voter program will be critical again this year. Strong early voting has saved several Iowa House and Senate seats the last few cycles. But voter mobilization can only do so much if there is a large enthusiasm gap between the parties. I also hope that Culver’s campaign has a game plan for bringing the dissatisfied Democrats home in November.

UPDATE: John Deeth doesn’t think the registration gains are anything to brag about, because they grew out of a divisive, still-unresolved primary.

SECOND UPDATE: Bret Hayworth notes the registration numbers for active Iowa voters: 661,115 Democrats, 615,011 Republicans and 683,817 independents.