If they were dirt poor, there would be little reason to suspect that there was some dirty dealing going on, and/or that John McCain was benefitting from financial deals that weren’t on the up and up.

I don’t see that wealth or the lack of it predicts criminal behavior at all. Yes, the wealth creates opportunities for investment that the poor can’t use, so the wealthy are more likely to have investments that we can check for conflicts of interst; but that’s not to say that the wealth increases the likelihood of “dirty dealing.”

The prejudices of the 19th century held that the poor were more likely to commit crimes, which offends our modern, egalitarian sensibilities. I haven’t figured out yet why a prejudice holding that the rich are more likely to commit crimes does not offend those same, egalitarian sensibilities… unless we’re actually just hiding Marxist dialectics behind a scrim of egalitarianism.