It's so hard to narrow it down to one.
In no particular order,
Lincoln, the Obama of his day, a radical elected by a narrow slice of the country who nevertheless pushed a devastating war on us, resulting in the deaths of half a million people,
Woodrow Wilson, the Obama of his day, an anti-Constitutionalist progressive,
FDR who was determined to get us into WW II against the country's wishes and against our best interests,
LBJ a loathsome, corrupt sleaze who put us on our current downward trajectory,
Eisenhower who sent federal troops to impose a second Reconstruction on the South,
Carter who turned Iran over to the islamist crazies,
Bush 41 who foolishly blundered us into a situation where Saddam Hussein thought it was ok to invade Kuwait then got us involved in what should have been a purely arab matter, leading to 9/11 ultimately,
Bush 43 who got us into two pointless wars, wrecking our budget in the process and of course
Obama, for all the reasons we know so well.