Steve King is the overwhelming favorite of Iowa Republicans to be their Senate candidate next year...and trails every Democratic candidate we tested against him by at least 7 points. It's the story of the last two election cycles for Senate Republicans.
We tested three different iterations of the GOP candidate field for next year, and King leads by at least 19 points in each one of them. In a four candidate scenario he gets 41% to 22% for Tom Latham, 10% for Kim Reynolds, and 9% for Bob Vander Plaats. In a three candidate field that doesn't include Reynolds he gets 42% to 23% for Latham and 19% for Vander Plaats. And in a head to head with Latham he leads 50/27.
King's substantial lead over Latham has a lot to do with his appeal to 'very conservative' voters- they prefer him by a 61/19 margin. But even with moderates King edges Latham 37/35. And it's not really about name recognition- the 75% of primary voters familiar with King is only a little more than the 64% who know Latham.
The problem for Republicans is that King would start out at a significant disadvantage in a general election. The most likely Democratic candidate, Bruce Braley, would start out 11 points ahead of King at 49/38. The three other Democrats we looked at lead King by substantial margins as well- Tom Vilsack would lead King 49/39, Chet Culver would lead 48/41, and Dave Loebsack would lead 47/40.
We tested 16 different possible general election match ups for the Senate- Braley, Vilsack, Culver, and Loebsack on the Democratic side against King, Latham, Reynolds, and Vander Plaats on the Republican side. The Democratic candidate leads in 14 of the 16 possible match ups, with the only exceptions being leads for Latham over Culver and Loebsack.
The strongest candidate other than Braley for the Democrats would be Vilsack. Besides his 10 point lead over King he also has advantages of 46/42 over Latham, 46/38 over Reynolds, and 52/35 over Vander Plaats.
Overall Democrats appear to start out slightly favored in the race to replace Tom Harkin, and if a hard conservative like King or Vander Plaats wins the nomination they will start out with a pretty substantial advantage. Latham would start out behind Braley or Vilsack too, but would at least be within striking distance.
Full results here