Harkin's announcement comes as five-term Massachusetts Sen. John Kerry departs to become the Secretary of State and West Virginia Democratic Sen. Jay Rockefeller retires. All three could be potential pickups for Republicans looking for a road map to take back the Senate in 2014.
"We have great candidates who will be running for re-election next year and with the grass roots excited, this senate seat is definitely in play for Republicans," says AJ Spiker, the chairman of the Iowa Republican Party.
In addition, Democrats will have to defend 18 currently held Democratic seats. A handful of those senators in states like Montana, Alaska, and South Dakota, will be fighting uphill battles in states that voted for Mitt Romney in 2012.