Take comfort that Abraham Lincoln was not really revered until five decades after his assassination. He actually did some amazing things given the times that he was in. Maybe Obama might have a similar place.
I look at FDR, Eisenhower, and Reagan as presidents who had a vision and could "force" the political process to achieve some of that vision.
On the Canadian side, I see Mackenzie King and Trudeau Sr. as great polital players that also accomplished things. Tommy Douglas was so instrumental is Canada's public health care system--even though he only led a third-rate party.
But methings times have changed such that no political leader can affect a similar change any more. It seems silly that we are still putting our hopes on a messiah.