The Radical warns against entering political discussions with Expat Americans, on the grounds that you might get a stream of anti-American vitriol in response. He points to a real problem, but one that exists even in New York. I'd say you just have to choose your conversation partners carefully. Sound them out with a few softball comments before you really discuss anything significant.
There's a certain category of expat (quite common in Amsterdam) with whom political conversation should be avoided. They're in Europe because they essentially hate America (though they'll pay lip service to American ideals) and if they were still stateside they'd be holding naked barf-in's and carrying "Bush == Hitler" signs. They aren't stateside, though, so they have even less contact with or understanding of America and they're railing against an imagined dystopia that has little to do with contemporary America; in particular, they have absolutely no comprehension of how 9/11 affected many Americans.
The expats who left in the sixties and seventies are the worst - they literally can't imagine that anything has changed in the past 30 years and their rants have almost no point of contact with reality.
You do encounter the occasional pro-American/anti-European Expat who is just as obnoxious and out-of-touch, but they don't seem to last very long before they repatriate.