Last week, in a meeting with Democratic leaders, President Trump called the government shutdown a “strike.” This was an enigmatic use of a hallowed term, although it might have simply been Mr. Trump’s confusion about the “blue flu” epidemic afflicting employees of the Transportation Security Administration, who are working without pay and registering their protest by calling in sick, and in some cases quitting outright.

Last Saturday, about 5.6 percent of the roughly 51,000 T.S.A. officers stayed home sick, the Federal Aviation Administration reported.

In contrast to a strike, blue flu — a condition that has also been known to afflict police officers — is a quiet form of protest, with no stated principles or claim for public attention or sympathy. At the end of the day, each worker goes home and calculates his or her ability to go another week or two — or months or years, as the president has threatened — without a paycheck and acts accordingly.

Since T.S.A. agents, who are among the most visible of the affected workers, make do on a starting wage of about $23,000 a year (with the possibility of going up to about $43,000), these can be hair-raising calculations: Skip the children’s dentist appointments and pay the electric company? Or try to get an extension on the utility bill and go without getting the car fixed?