What is "constitutional" has always been fairly arbitrary. The Supreme Court just does whatever it wants while providing some legal rationalization.

To those replying to this comment: given that the FBI checks were part of McCarthyism to go after political opponents employed by the federal government, how would you feel about having the feds show up on your doorstep to ask you about your questionable recent voting history and political activities because you are, say, a bureaucrat for the Department of Transportation?

Are you doing anything Unamerican, citizen? Do not resist. If you have nothing to hide, you have nothing to fear, right? Hmm, says here you got an abortion a few years ago. The fatherland needs workers, why would you deprive us? And over here it says you attended a pro-terrorism (pro-Palestinian) protest. Blacklisted and flagged for monitoring. Go about your business. Enjoy minimum wage and being unemployed.