Thanks. I see where "the US are quite capable of destroying Detroit . . . " isn't exactly the same as "destroying themselves." Thing is, in an American political context, mentioning "Detroit" and "destroying" in the same sentence is virtually always racist coding, unless there's a very clear explanation to show the use is literal. Thinking Glen Beck's comment about nuking Detroit and starting over because Hiroshima is so nice now.
The whole idea of dog whistling is saying something bigoted you know people who agree with you understand, but not so explicitly that you can't insist you meant no harm. That's why I asked. I'd have thought regular contributors to a thread on American politics would understand common dogwhistles, but hey . . .
Okay, I'll accept it was said in ignorance. A simple "I/he didn't mean it that way" or "I didn't realise its sounded like dog whistling," would have sufficed. But nearly a page of defensiveness and invective? Jesus wept.