because of the shutdown, how far in advance should I arrive for a flight?

For national flights be there at least 3 hours earlier because TSA staff is working with a skeleton crew due to personnel "calling in sick" in response to ongoing government shutdown and also because of ongoing airport construction which may have you running to another terminal instead of the one in your flight itinerary. Make sure to check in luggage at individual kiosks and / or customer service desks and to print out your boarding passes at home 24 hours prior to flight or at terminal if not able to use phone scan bar and / or printouts. Have a safe flight.

Give yourself 3 hours just to be safe.