1. China
2. Islamic terrorism
Why is China a threat?
It is a present and long term threat to US world dominance. Therefore, enemy No.1Enemy? No. Last I heard we are at peace.
Present- Lol, they have no territorial ambitions outside their own backyard, military spending way below ours.
Long term- Low birthrate, slowing economy, headed toward being the next Japan. Is Japan a threat to US dominance?
The only threat posed is that of war which would do tremendous damage to our country and possibly even destroy it, plus earn the enmity of 1.4 billion people.