I think Biden does make it difficult for McCain. He can't go with a light-weight like Pawlenty or a new-to-politics Fiorina or Whitman. Biden would shred them in the debate and with McCain's age being such a factor, they don't meet the ready to step in test. You have the Christian right revolt if he picks a pro-choce candidate like Ridge or Lieberman.
Romney is all that is left and his so-called economic "strength" is a double-edged sword. He can be attacked as the CEO that cut lots of jobs to make himself extremely rich. He also has many homes and can be tied to McCain with the rich, out-of-touch elitist message to bring back the working class to the Dems. No wonder they are in favor of the tax cuts that favor the rich. Will his economic plans favor the rich and leave the middle class and poor struggling? I think we already know the answer to that.
Many on the right are uncomfortable with the Mormon issue. And McCain opened the door with the commercials of Clinton and Biden criticizing Obama in the primary. Anybody remember how nasty it got between Romney and McCain in the primary? LOL He is also weak on foreign policy/commander in chief and not ready to take over. How about the criticism of Obama admitting his "weakness" in foreign policy by picking Biden. Wouldn't this pick show a "weakness" in McCain on economics which is the #1 issue? If fact, I think Biden will emphasize how Obama has been in the lead and has been proven RIGHT on foreign policy over and over again starting with his speech in 2002. Every attack McCain tries to use against Obama applies to him even more.
McCain is grasping and even floating the idea that Colin Powell is being vetted. I think this could backfire HUGE. Powell could come out and say he is not interested on being on a ticket with McCain and even endorse Obama. He has stated he will wait to choose his candidate until after the conventions. They must be peeing their pants not know what to do.