Why Mark Warner isn't running

Just conjecture at this point, but makes about as much sense as anything else:

Why Warner Isn’t Running (eVote.com)
At the moment, we can’t see a specific trail that leads from Warner’s Nextel landfall and his present hiatus from politics. But clearly there’s more to the Warner pull-out than his announced reasons, and the trigger for his withdrawal may have been this past week’s crescendo of CEO resignations, terminations, and early retirements.

Warner may have chosen to take himself out of a race because it was only a matter of time before his previous financial history did so.