First, he's really not running against Mitt Romney (or whomever), but against Mitch McConnell and Eric Cantor, as Michael Tomasky notes. About 60 percent of moderates in Florida and even one-third of conservatives think the Congressional GOP is deliberately stalling legislation that would help the economy, he says.
However, he offers a caveat: Democrats in general and Obama in particular have to handle this correctly. And, so far, even in his moments of actual or feigned outrage, Obama has struck me as nothing like Harry Truman, giving hell to the "do nothing" 80th Congress.
Second, Obama IS running against a GOP set of mutts: either a Mitt Romney who inspires the party wingnuts, at best, no more than McCain, or a wingnut who drives off more moderate voters.
Tomorrow's off-term elections, coupled with a Democrat (of sorts) holding on to the West Virginia governor's mansion, should give more clues about Obama's chances.
UPDATE: Prop 2 won going away in Ohio. And, spermatic personhood got its butt kicked in Mississippi. So, Dear Leader has some hope to cling to.
But, back to Tomasky. While Obama is great at branding himself, it still remains to be seen how he can handle "going negative" with style. And, re Ohio, union workers are enthusiastic about their rights, not necessarily about Barack Obama.