Wait a min....you have a computer in the bathroom? LOL
That was my first thought, too. : )
Girlfriend, is it not YOUR dinner table? Get out there and eat! You do not have to respond to everything an idiot says. If that person has to stay, there's nothing wrong with saying you don't want to discuss politics today.
If you have the authority to kick that person out of the house (are you at your mom's?), then hand 'em their coat and tell 'em good night. Have some egg nog and relax. Last thing anyone needs is a liberal on the holidays.