Why?
MO is an uphill climb for Obama. While it may have been a close loss in 2008 it'll be an uphill battle here.
Obama has a healthy national lead. He's not going to lose MO by nearly double digits while he has that.
Rasmussen uses a "likely voters" poll that assumes that previous voting is the strongest determiner of what persons will vote. It seems logical that someone who hasn't missed a Presidential election in sixty years is nearly a sure thing to vote because of a personal proclivity to vote (reasonable until you think of the Grim Reaper removing such people from the electorate) and that someone who has never voted won't vote this time. Of course there are new voters in almost every election.
The younger voters are much more liberal-leaning (and D-voting) than any other group of age-based voters. Remember that the Democrats (and unions) are going to try get every possible voter out to vote. If they find that 20-year-old "Fluffy" is in a D-leaning household then they are going to make some effort to register "Fluffy" to vote until "Fluffy" is shown to be a cat.
