Everything that is "shut down" at the moment is by definition non-essential, or it wouldn't be shut down. The only thing on the whole list of affected agencies that gives me a moment's pause is the Coast Guard.
Yes, this. The FFs would roll over in their graves if they knew all the op pies the feds were sticking their fingers in.
For the moment federal income tax deposits are coming into the treasury at a reliable pace at about 98% of prior year, as time goes on this will diminish with out oversight & enforcement. We've got some time to wait before seeing the decline as long as every business stays the course on full compliance.
Return processing needs to occur, currently, the form 940 & 941 will be due by 1/31/2019, though many are filed electronically, a good portion are still filed on paper, clerks are needed to processes these documents, once that deadline passes, form 1120/1065/1041 will be due next, then finally form 1040 by 4/16/2019
The 1040 series returns also come in electronically at about 85% while 15% are processed by clerks, these returns need to be processed timely to ensure prompt payment of refunds about 400 billion in the course of a year. Late payment of refunds incurs credit interest @6% to the taxpayers, this could be a HUGE cost to all taxpayers. Those who owe and don't pay need direct interaction, first by letter (clerks involved) and on occasion direct personal contact by phone, business or home, these enforcement folks (like myself and 30,000 others) ARE NOT considered ~essential~ at the moment, but as the economy begins to suffer that decision could change.
POTUS has committed to this shutdown lasting as long as it takes to get the wall funded, and it could go several months and possibly a year in his own words, BTW, I support his position and even wrote him a letter of my personal support, so hen he says he has the backing of affected FED's he is telling the Gods honest truth. I'm anxious to get back to business, there will be a lot to catch up on when I do get back.