Obama now had one million donors. This article points out why that threatens the Washington establishment in ways much bigger than "empty rhetoric" does. http://www.consortiumnews.com/2008/022608.html
Because Obama doesn't owe the money people they don't own him. Interestingly, because they've misunderstood what's happening, they started to band against him way too late. Under normal circumstances they'd all flock to the GOP candidate in order to preserve their power. But wait! They weren't paying close attention there, either!
While McCain is hardly the reformer that Obama is, he's still highly unfavorable territory for the money power people to work with. He may be slightly better, from their point of view, than Obama, but that's still just plain awful for their interests. It's like a condemned man having to choose between a hanging and a firing squad. Some choice.
All of a sudden they've got no buddy in the White House, either way! Oops.