Which country is the biggest threat to the U.S. or its interests?

[Kevin]

I'd say a tie between Iran and Pakistan.

In Iran, Islamic-Fascists are solidifying their hold over the country's institutions. As well as posing n external threat to the US, Israel and other nations through regional meddling and support for terrorist organizations combined with a drive to obtain nuclear weapons. In Pakistan, you have an Islamist insurgency in the form of the Taliban as well as some other groups like Al-Qaeda creating regional and internal instability. However the Pakistani government and armed forces which are riddled with corruption and incompetency combined with subversive elements among their ranks. All of which poses the possibility of toppling the government and putting into jeopardy it's control over Pakistan's nuclear arsenal.