I hate to think about this too, but in regards to your quesiton...

If its after the election, as stipulated in our Constitution, the Vice-President-elect Biden would ascend to the top office on the day of Inaguration. Afterwards, he'll nominate somebody for VP and Congress will approve it. The last episode of THE WEST WING covered this, FYI.

If its BEFORE the election...more likely, the ballots would already be finalized with Obama/Biden, and wouldn't be changed. But Biden would then be asked, and he'll accept, to take over as the main candidate. He'll ask somebody within party ranks, i.e. Hillary Clinton or Bill Richardson, to take over for VP.

You all might remember in 2000, in the Missouri Senate race, when the Democratic candidate was killed in a plane crash a few weeks before election day. His name stayed on the ballot, and his wife took over. The GOP challenger John Ashcroft (yes, THAT John Ashcroft) couldn't attack an opponent who was dead, nor attempt and be slammed for criticizing a corpse. The wife won.

I'm just saying, Biden would probably win, if simply for the sympathy vote. But if the assailant is White...Pizzaboy's assertion of urban racial riots is a troubling stark-real possibility.

McCain may be partly blamed, fairly or not, for the murder if because his campaign stirred up alot of bottled-up tensions and angers within the extreme-fringes of the Republican Party out of the closet, and into the daylight of his rallies. Notice how a prominent black Congressman this weekend compared McCain to George Wallace.

Notice how McCain stopped his "Who is Barack Obama?" speech-line after many people yelled "Traitor!" "Terrorist!" "Arab!" and other shit at his rallies. Hell, you all read of how after trying to correct a woman that Obama wasn't an Arab, his own supporters BOOED him.

Now mind you, alot of psycho-loons of the Left have been out there as well, being fucking ugly, most prominently the 9/11 "Loose Change" Conspiracy advocates and the ultra-anti-war factions. They're loud assholes, and even liberal Bill Maher threw those Loose Change folks out of one of his tapings last year.

But like that shit said by the Virginia GOP leader above...the news on the McCain campaign isn't that McCain has the better economical plan or new pitches, but that of the crowds at his and Palin's rallies.

Hell, even Charlie Crist, the popular GOP Governor of Florida, is publicly distancing himself.