They said that about Harry Truman also. He turned out ok in the history books.
So let me get this straight. According to you, Bush will turn out to be OK in history books, in spite of pointless invasion of Iraq and untold number of deaths as a result of it. Also, in spite of being responsible for two huge economic meltdowns, the recent one the worst meltdown since the Depression.
Obama however, being in the office a little over a year, not having started any war, slowly cleaning up the gigantic mess left by Bush and the Republicans, is already the worst president ever, and nothing he does in the next six years will change that assessment.
Are you a presidential historian? You must be to issue such definitive, authoritative assessment.