Bush II, though Reagan is close.
Harding. What the heck's wrong w/ Reagan?
Massive Deficit Spending,
Growing Government Bureaucracy, Iran-Contra, Ignoring AIDs, ill-advised alliances (Iraq, Mujihideen, etc.), "Homelessness is a choice", Appointing Crooks and Hacks like Ed Meese, Making Taxes more regressive, and allying with the Religious Right. And that's just for starters.
Oh and the claim that he "won the Cold War" is a ludicrous. The Soviets Union was doomed from the get go, as all regimes of their ilk are. The only way they might have survived is if they made serious reforms early on (similar to China), and if they did that they'd no longer be Communist. Reagan is the most overrated President in recent memory, maybe of all time.