Is it possible that John McCain is the Carrot Top of political candidates? He keeps using props to keep his failing campaign propped up. First it was Sarah Palin, whose selection was hyped as the magic bullet that would seal the deal for him. In fact, Palin is probably a net negative for McCain, keeping the base for him but turning off independent women who see the gibberish Palin spouts. But now that the Palin effect has faded, he needs something new.
Enter Joe the Plumber, and the mythology around him aside, he is now as much a running mate of McCain as Palin. He's now a part of McCain's stump speech and there were stories that McCain asked him to campaign with him, along with the other hanger-on crutches like Lindsay Graham and Joe Leiberman.
McCain can't stand on his own. Again.