No.  You may still cast your ballot as you please.  Bloomberg is funding Brown's election, not Brown herself.  Bloomberg does so because of Brown's past record of supporting sensible and needed restrictions on gun purchases and civilian ownership of arms appropriate only to battlefield use.  That's fine with me.  I don't want the local delinquents to own guns, and I don't think anyone not in the military needs or should have weapons capable of killing sprees.