From about 2003-2007, traveling abroad as an American could have been more difficult than before. A lot of places you’d go, the people were suspicious or even angry at US foreign policy, particularly the Iraq War. Not that they would necessarily be rude to you if they knew you were American, but there was just that little bit more of a general chill, compared to before.
Obviously, this doesn’t affect people from Long Island who tend not to “cross well-understood geographical boundaries” (Kurt Vonnegut), and I get the attitude that “it doesn’t affect my life so I don’t care” – But American prestige and credibility abroad do matter even if the effects aren’t direct nor tangible.
I’d forecast that a Trump Presidency, and a bull-in-the-China Shop, transactional Foreign Policy (you pay this, you pay that Mexico and Japan; bye NATO), would be significantly more damaging than the Iraq War.
Americans should prepare to be greeted with increasing suspicion abroad.