Shouldn't be, according to USPS they're an independent entity not federal tax funded and thus aren't affected by the shutdown.
I'd be curious to know how soon/late I can expect mine as well.... last I've gotten any updates, USPS says "processed through a facility in KIEV PI-2, UKRAINE at 10:28 pm on December 29, 2018", and Ukraine's postal service says "Departure from outward office of exchange (29.12.2018 22:28:00)" (seems both messages refer to the same event?)
I know it's only been 11 days since then but meh I am impatient and excited for my ED to get here XD