OK, so I've been seeing the smug 'holier-than-thou' way Republican pundits have been responding to Obama's picking Joe Biden as VP, and I think we need to respond by giving them a little of their own medicine. They really like to play the "attack no matter what" game, but there is no reason we can't do the same.
From here until the day of the pick, Democratic strategists and pundits need to repeatedly express the strength of Mitt Romney as a running mate for McCain, based on his "economic credentials", polling data, etc. Then, IF McCain is actually stupid enough to pick Romney, we shift directly into "how many houses does Romney have?", and fit Romney into the "McCain is out of touch" argument.
If, however, he picks someone that isn't Romney, we say something along the lines of:
"You know there's been a feeling among the public building that John McCain is too wealthy and out of touch to understand the problems of ordinary Americans, and I see his rejection of Romney as a surprising and Frank admission by the McCain campaign that that viewpoint has validity."
If he picks Lieberman, we should point out that it is surprising that the nominee of the Republican party would turn his back on the very group of voters that has delivered that party to the White House for the last two elections. Stress that it's a slap in the face to evangelicals, and then point out what a good fit it is, and point to all of the McCain/Lieberman flip-flops, like Lieberman saying he wanted to help elect a Democrat in 2008 to get elected in Connecticut, etc etc.
I also think we need to point out something Obama touched on in his speech today, namely that Biden is the straight shooter that McCain pretends to be.