The main point is don't get hooked when LEOs are on a fishing expedition.

I view this as very similar to getting detained at a sobriety checkpoint and being asked "Have you had anything to drink tonight?"

If you answer "no" and they detect alcohol on your breath via their special flashlights, you've just lied to a cop. If you say "yes", you may have just incriminated yourself. So, I've taken the approach to simply decline to answer that question.

It's not the same. The checkpoint officers don't ask, "Have you EVER had anything to drink and driven?"

Even if you answer yes there are no consequences. A visitor admitting past drug use however faces being turned back and banned.

You are comparing two entirely dissimilar situations - an answer to a question from a police officer regarding current conduct at a sobriety checkpoint where your response can be easily verified versus an immigration context where you know there is no evidence of your past conduct that can be used against you. In the former, I’d keep my mouth shut. In the latter, no way I’m admitting to past use of illegal narcotics.

If you weren’t arrested or charged with illegal drug use, if there are no medical tests or records that document your illegal drug use, and if you weren’t stupid and bragged about such use on social media, what can the USG use against you?

Access to e-mail or other files/communications that include indication of illegal drug use? How the USG gets the information about illegal drug use doesn’t change my question.

My question was about whether the government’s later discovery/recovery/utilization of information about illegal drug use could still be used to undo the immigration/naturalization status of a person who willfully and falsely denied illegal drug use during the process of seeking an immigration status change or naturalization.

If you were stupid enough to admit to past drug use in any form of written communication, then yes, you shouldn't lie to a Customs Officer upon entry to the US.

Just because the government might allege at a later date that you lied to the CO, what's their proof? What if they are going on the word of some third party who mistakenly frames you as a drug user?

The point that jumps out at me, using the checkpoint example, is that individuals like the guy in the article should think ahead about what to say rather than try to think on your feet in front of an immigration official. Perhaps he got some bad advice? Perhaps there are lots of pictures of him on social media?

I would hope that the government doesn't just take someone's uncorroborated word for it (maybe unless they have a number of friends, family, etc. saying "yep I used to blaze it with that guy every day"). But what are the situations where the government goes to the effort of interviewing family, friends, co-workers, etc. of a foreign citizen in, or arriving to, the US? Does it occur for green card applicants or those going down the citizenship path? It seems like whatever those circumstances are would be about the only common situations where it's even theoretically a concern that someone would "rat you out" or that a private communication would surface, aside from some other Federal dealings that aren't common for most non-citizens.

Otherwise if, as noted before, there is no public record of it, there's just no realistic way the government will ever find out. They don't send out investigative field teams for every tourist or short-term business visitor or similar, who comes to the US.

Two relatives of mine were sponsored by my family to come to the US. When they arrived at MSP for their first trip to the US, we got called by CBP’s predecessor at the airport and were asked to confirm some information, none of which involved drug use; and there was some back and forth. Later, when the same relatives were changing their immigration status for the third+ time, there was another effort made to confirm some of the same sort of information asked by CBP’s predecessor and/or State. While it is very far from common, it’s possible and does still happen.

That said, it’s been very uncommon for LPR status and — even way more extremely rare — naturalization status to be undone due to discovery of material misrepresentations made earlier during an application seeking travel and/or entry/admission and/or change of immigration/citizenship status. But it can happen, and it may just require some in the relevant positions of authority to want to make it an issue and it could become an issue even as it may not have been a priority or even considered relevant for many years or decades before.

I think you outlined the scary part.

"Not that I recall" seems like a safe answer but I'm a senior citizen and can get away with being forgetful.

Here is some helpful guidance for dealing with a law-enforcement or inspector general questioning session. Whatever it is that you told them the first time you are questioned, if they come back for a repeat session, you don’t change your story at all. In fact, when they try to get you to re-answer the same question they asked you before, your response should be “the same thing I told you last time, officer. You know, that questioning was a long time ago and I don’t remember the events as well, as time has passed.”

When you are being requestioned about the same event, the officer is almost always trying to get you to utter an inconsistency so it can be used against you.

One would think that. But saying "I don't recall" when you do in fact recall is lying. For example, if the CFO of United and were asked if ever he ever heard the the CEO of United say "we need more flights to countries like Norway and less flights poophouse countries" and the CFO said "I don't recall", most people would think, "gee, I'd remember if I heard that or not". Many people would also probably think, "gee, I'd probably remember if I'd tried marijuana at all in my life". Sort of like, "do you have any drugs in your car?" "Not that I know of".

I did quality my response.

I do like being able to say those little phrases like "I am having a senior moment" - the kids at work bite on it almost every time...

Little bit of a sidebar, I am not really certain what that question (as phrased) has to do with a Visa app nowadays. If they ask something like "are you currently, or have you within the last 45 days, used any illicit substances or illegal drugs", I might could see that being the norm as it shows current behavior contrary to what most may deem acceptable. What someone did 30-40 years ago as a knucklehead in high school or college, can have little to no bearing on what that individual is like now. I guess maybe they could use it to try and establish a trend of behavior that is unacceptable in the eyes of the government.

I don't recall a specific rider or entry indicating that previous drug use is a disqualifying factor - of course, it has been years since I read up on the intricacies of immigration/Visa/entry process., so I could be mistaken.