So here's a fun travel puzzle: What happens to airport security when the agency that runs it doesn't have money? That's the situation travelers are facing as the Department of Homeland Security shutdown enters its 10th day, and the answer is... complicated.

Let's start with the good news. The Transportation Security Administration had announced it was temporarily rolling back its PreCheck program—you know, the one that lets you keep your shoes on and your laptop in your bag—because of a shortage of funds. After widespread criticism from travelers and the travel industry over the weekend, the agency reversed that decision. So yes, PreCheck lanes are open.

Now for the less-good news. The Global Entry program, which lets pre-approved travelers use expedited kiosks when entering the U.S., remains shut down. Those lanes are closed. So if you're flying internationally, you'll be going through the regular customs line like everyone else.

And here's the reality check: Even with PreCheck open, things might not be smooth sailing. TSA workers are currently working without pay. The agency has warned that lines could still face delays and disruptions, and there's always the possibility that employees might not show up for work when they're not getting paid. It's not exactly a recipe for peak operational efficiency.

The bottom line for travelers: Plan thoroughly and expect some level of disruption. This isn't business as usual.

So why is this happening? It comes down to funding. Lawmakers failed to reach an agreement on funding for DHS, with some demanding changes to the agency following multiple fatal shootings involving Immigration and Customs Enforcement agents. President Donald Trump had earlier signed a $1.2 trillion funding package that ended a brief shutdown and approved funding for most federal agencies through September 30, but DHS's funding was approved only through February 13. That deadline has come and gone.

This isn't the first government shutdown we've seen, of course. Last year, the U.S. recorded the longest government shutdown in history—43 days—which caused approximately $7-$14 billion in real GDP losses and forced nearly 900,000 federal employees to work without pay or be furloughed.

For now, the TSA is trying to keep things running as normally as possible under difficult circumstances. But when the people responsible for airport security aren't getting paid, and the agency funding them has expired, "normal" becomes a relative term. Pack your patience along with your carry-on.