Businessman Mike Sherzan (D) announced he won't run after all for the seat after announcing a bid earlier this year. He cited health problems as the reason he won't run.

"There's a real desire to see a problem solver representing our state in Congress. I had hoped to be that person. Unfortunately, due to personal health issues, my campaign cannot continue," he said in a statement emailed to supporters. "I have made this decision based solely upon my individual circumstances and what I believe to be in my best interest and that of my family. Ending my candidacy is very disappointing to me personally."

The district is a pure toss-up — President Obama narrowly carried it in 2012 while Latham defeated fellow Rep. Leonard Boswell (D-Iowa) by a comfortable margin. When Sherzan first decided to run, it appeared that Latham was leaning towards a Senate run, something he's since ruled out.

With Latham running for reelection, the seat appeared to be a tough one for Democrats to pick up. Sherzan's decision further complicates those hopes, though Democrats do have other potential strong recruits in the wings including former Iowa state Sen. Staci Appel (D).

This post was updated at 4:05 p.m.