Nixon's a new face on the national scene, but he's a career politician in MO and is not someone who can credibly label him as an "outsider". He's got executive experience, but no foreign policy chops. He's a logical VP pick for Hillary Clinton, and he might help expand the map.
I don't see Nixon as a credible Presidential candidate, and I really don't see him running against Blunt unless he's promised loads of money. I wouldn't be surprised if he opts out of running against Blunt in the hopes of being selected for the national ticket. I would be slightly surprised if Nixon were to beat Blunt; MO is trending GOP and I don't see Blunt losing in such a nationalized election. Yes, Claire McCaskill clobbered Todd Akin in 2012, but look at the "help" Akin gave her.
If Nixon doesn't run against Blunt, who is the Missouri Democrats' best choice?