Air Traffic Controllers, TSA Agents and CBP officers are all considered vital employees and will work during the shutdown. They will also get paid--eventually.
Mmmm, mostly true, but…
All the above are indeed required to continue working thru any shutdown - without pay. Those who are direct federal employees will get paid eventually, but those who are contractors MAY not (and there are a lot of them). The administration has been threatening to “furlough” or lay off or outright fire some federal employees and has stated that if they’re not working, they’re not going to be paid. Still lots of unknowns. Lots of posturing going on, nobody’s happy.
I occasionally have to deal with FAA staff personally. I can share that there has been a long-standing, ongoing morale problem (I’d call it a crisis) among many FAA employees (including air traffic controllers) - and that was before they were required to work without getting paid (remember, these same people were told last spring that they should quit and might be fired eventually). This isn’t going to help.
Employees working but not getting paid often dislike doing so (surprise!). In previous shutdowns, more than a few employees called in sick as a form of protest, resulting in long lines at TSA screenings.
If this goes on a while (and there’s no sign it’s going to be settled anytime soon) things will become increasingly strained. If nothing else, I’d plan for more time when going through TSA screening. Hopefully, that’ll be the extent of any troubles.
I’m currently in Europe and fly home in about 10 days. I’m not anticipating any issues re-entering the country, but as the shutdown stretches on, I would expect at least some delays and disruptions to become unavoidable. Pack patience.