• Democrats held their convention in Charlotte in 2012 when they re-nominated Barack Obama on his way to re-election.

Democratic Sen. Jeff Merkley of Orgeon was in Iowa last weekend, his third trip of the year. He's rumored to be considering a potential presidential run in 2020.

• Three governors have already been in Iowa. Montana's Steve Bullock, Colorado's John Hickenlooperand Washington state's Jay Inslee said last weekend they are considering 2020 runs, per CNN.

Bonus candidate: Former Attorney General Eric Holder is "seriously considering throwing his hat into the ring for a 2020 presidential bid," sources close to him told April Ryan, White House correspondent for Urban Radio Networks.