With races for four major seas up for grabs, a report shows more than 24,000 Iowans registered to vote as Democrats last month.

The last time Democrats saw a voter registration increase of this magnitude in the month of June was back in 2006. Democrat Chet Culver won the party’s competitive gubernatorial primary that year, en route to winning the governorship that November.

In one of the races, Republican Rod Blum of Dubuque is seeking reelection in the first congressional district. That’s where Democrats hold a roughly 23,000 voter registration edge over Republicans. Abby Finkenauer of Dubuque is Blum’s Democratic challenger. While incumbents are heavily favored to win congressional race, this contest is often listed as a toss-up by national rating agencies.