That is a concerning thought... indeed it's not just Putin, but also Xi Jinping, Kim Jong-un, and others. What if they all decided to attack at once?
The USA certainly wouldn't be able to handle it alone. And whatever problems the current administration might have, that's also true of past administrations: the USA has never been powerful enough to take on the entire rest of the world on its own (except perhaps a brief period in 1945-49, when they were the only ones to have a nuclear bomb). Instead, I believe there would need to be a united response from the entire Western world.