We tried that in both World Wars.
We came in late to WWI to break the stalemate (and reap some benefits, a fact that most people seem to politely forget), but we had no interest in jumping in at the beginning. Ultimately, we knew a prolonged war has hurting us, too, so we took action. And it was costly.
Same thing in WWII. Even when the threat to us was obvious, we were so bitter from WWI that the American people wanted no part of the war in Europe. If Roosevelt wouldn't have deliberately let the Japanese kill our men at Pearl Harbor (minus the carriers, of course), we probably wouldn't have gotten involved until well after Britain fell and nearly the entire world's industrial might was turned against us.
The fact is this: Germany is too dangerous and too treacherous to turn our backs on. U.S. troops are stationed there not to protect Germany from Russia, but to protect the rest of the world from Germany. Think about that.
Nowadays, although Nazism is enjoying a resurgence there, the real danger is Marxism. A Germany under a new Stalin is no less a threat to the world than a Germany under a new Hitler.
Personally, I hold the German people in very high regard. They are an amazing and capable people who literally have the power to take over the world. And that's why I would never turn my back on them.
Not only should we maintain garrisons in Germany, we must have a (extremely secret) policy of moving quickly (and anonymously) to remove or assassinate any new German leader that demonstrates the charisma and ambition that may move Germany toward another bloody campaign of conquest.
As much as I despise Gerhard Schroeder, he's a better leader for Germany than someone who is competent and potentially dangerous.