Why are people spinning the loss of Specter to be Obama's problem?

I think the Specter loss was a referendum on himself. I don't care what side you're on, this guy is a joke and most didn't like him. The rest of the elections (and the ones to come) are/will be a referendum on Obama...or rather his merry gang of radicals trying to ruin this country...since Dems and maybe even inbent Reps are sure to lose.