[dmiladinov]

According to Wikipedia:

Exile means to be away from one's home (i.e. city, state or country), while either being explicitly refused permission to return and/or being threatened with imprisonment or death upon return.

So he's probably not so much worried about whether or not he can return to the U.S., but rather what would happen to him when he did.

http://en.wikipedia.org/wiki/Exile

[mpyne]

Even so, the imprisonment would be because he returned per se. He may come back and the jury says "not guilty" and walk off a free man, after all.