Which countries are the biggest threats to the United States?

[Middle-aged Europe]

Threat in what way?

The capability of physically destroying America through nuclear weapons (at the expense that the attacker will be destroyed as well) is currently possessed by Russia and China. I guess Russia is more likely to push the button, since Putin alone would make that decision while in China's case it would ultimately fall to the seven guys on the Politburo Standing Committee which increases the possibility of a veto. Either scenario's likelihood is rather slim though.

At present, the country which is most likely to do something that would actually result in the deaths of American citizens is probably Saudi Arabia via their funding of extremist groups etc. Which is also why it is pretty smart of you guys to sell them F-15E Strike Eagle's right now. I'd also say Iran is a bit less likely because them being Shia makes things much more complicated: they hate at least half of all Islamic terrorists themselves. Plus, their current president at least counts as a Reasonable Authority Figure.

And the greatest economic threat to America is of course China.