Tom Schaller highlights the most lurid detail in that Salon article on George Allen:

Shelton said he also remembers a disturbing deer hunting trip with Allen on land that was owned by the family of Billy Lanahan, a wide receiver on the team. After they had killed a deer, Shelton said he remembers Allen asking Lanahan where the local black residents lived. Shelton said Allen then drove the three of them to that neighborhood with the severed head of the deer. "He proceeded to take the doe's head and stuff it into a mailbox," Shelton said.

And I think Schaller is absolutely right about this:

This may be the episode on which Allen’s Senate career (I think his presidential career has gone the way of the deer’s head) may turn, for two reasons. First, because an incident like this, if true, is not only grotesque and craven, but reveals a general hatred rather than an anger directed at a specific individual....If Shelton’s account is true, for Allen any black suffices for intimidation and ridicule.

The second toxic element here is the verifiability of the event....If Scherer or Lizza are able to document this incident, or if a credible source comes forward to confirm, get your butter and jam out, folks, because Allen is toast.

I'll go further: if this is verified, then Allen is not only toast--he becomes a major liability for the Republicans as a whole. At that point, every Democratic candidate in every state or district should be asking his or her Republican opponent if they think someone like George Allen should be in the Senate. Get them on the record. If they toss him overboard, that's a scalp for the Democrats. If they don't--if they try to weasel out of answering, or are supportive of Allen--it becomes a club to beat them with. Implicit racism is (sadly) often a political positive, but explicit racism is taboo; forcing the GOP to deal explicitly with issues of racism can only hurt them.