Imho, it's not xenophobia as much as "foreigners don't vote, who cares about making things better for them".
Tourists bring lots of money which they spend in the shops, hotels, restaurants, taxis, etc of voters.
Voters should be voting to encourage this.
Especially given the current economic climate, you'd think they'd want every dime they could get!
And I think the lack of foriegn travel by a lot of US citizens has somthing to do with it. If you have gone on forign holidays and gone through customs your self you might be more understanding when your doing that job.
I'd say it's a mix of that, protectionism, and 1930's isolationism being mixed into a healthy, toxic brew