President Obama did have a supermajority in the Senate. It was only briefly, and I don't exactly know that I'd call it "functional", but it's a fact that he had one.
And even if he didn't have a supermajority, the Democrats held 58 or 59 seats, functionally (not counting the Franken debacle or Byrd's hospitalization) for two years.
If you're such a poor leader that you can't get anything done in two years despite the fact that your party holds the both House and 59 seats in the Senate then you're a C- president at best.
Thanks for bringing this up and strengthening my case (at least in my own mind). I'm now absolutely convinced that C- is more than fair.