The radioactivity alone would claim a fair amount of lives. Wouldn't destroy all of the US but a very large amount, not to mention the mental state of the country after a disaster like that.
That wouldn't stop more nukes from being launched. Both sides had enough nukes to destroy the world many times over.
Americans did. It's hard to argue otherwise, immediately after the war. We had 50% of world's production capabilities and everyone owed US money. I don't know if Kennan's legacy helped or hurt America after-wards though. I'm still on the fence with containment. It's reverted us back to a "Big Stick" policy that's cost Americans money, lives and prestige decades after WII. On the other hand, Russia didn't mind supporting communist uprisings. In that sense, I'm not sure if we won. Because of our overwhelming victory in WWII, we were/are "compelled" into defending the western world. We've been fighting proxy wars since, and at an unsustainable rate in terms of personal and money. Japan, Germany, Italy and the rest of the western world feels no such obligations.