The Association Game
For a few reasons I find it an odd choice of things to run out. First, if the Democrats want to get "down and dirty" with the Keating 5, they'll be reminded that 4 of the 5 were Democrats. The only one of the 5 to be officially censured by the Senate wasn't McCain, it was a Democrat (Alan Cranston).
John will probably bring out the Keating 5 special investigator, Robert Bennett, who'd recommended no charges to brought, or reprimand given to McCain. Bennett has said on many TV shows, and in his own book that McCain was charged only because the Senate Ethics Committee (chaired by Democrats) didn't want it to be a "Democrat's only" scandal.
The other thing that could cause the Keating 5 issue to backfire on Obama is the aftermath. It would be easy to see why McCain could have gotten bitter, and been a pain in the ass for Democrats after they toss him under a bus to make themselves look less bad. Instead, he spent the next 11 years working with Democrats to come up with a workable (though questionable) campaign finance reform bill.
Obama has no such story to tell. He can't tell, legislatively, where he's taken a stand on anything unpopular with his party. He can't say "Here's where I made a mistake, and this is how I worked to fix it". McCain can say that, and has the laws to prove it.
The other problem for Obama is that playing the "associate game" with McCain is probably a minefield he should stay out of. Amy Geiger-Hemmer has a nice piece up with some of the questionable characters associated with the Obama camp. I don't agree that every name on her list should be there, they are very peripheral players in the Obama world, but other should bother you when you read about them.