Probably won't ever affect TSA background checks, but if you ever submit for a DoD security clearance, expunged doesn't mean its gone. They can always find stuff about you if they want. The key is that you are trustworthy. I have an underage drinking that was plead down to disorderly conduct. I always report it as exactly that. If they ask about law enforcement issues, I bring it up. The key is that your comments and application match the background check.