Interestingly, 'clandestine' doesn't seem to be defined in US law; Black's law dictionary defines it as 'secret or concealed, especially for illegal or unauthorized purposes.' The law does ban such activities conducted 'on behalf of a foreign power,' which latter definition is so wide in scope as to encompass all sorts of people who might never have considered themselves to be such.
https://www.law.cornell.edu/uscode/text/50/1801
Simply having too high a degree of curiosity about certain parties and gathering publicly available data could easily be made to qualify in the hands of a creative prosecutor (and I anticipate prosecutions getting a lot less rigorous and a lot more creative in many jurisdictions real soon now).
Of course they could still lie but you can't be investigated just for your protected speech.
I'm not sure that curating a lot of information - a private library, if you like - constitutes a speech act per se.
Suppose, for example, that I wished to dominate the market for some collectible item and assembled a large volume of information on the market and its participants, but chose not to publish or advertise its existence so as not to tip my hand to competitors in that collectors' market. I would, by definition, be engaged in a sort of clandestine intelligence activity - albeit a wholly harmless one. I'm really not sure if the collection of such information is protected by the 1A.
You'd think so, but I can think of many persuasive arguments to the contrary. There's no federal law explicitly protecting the privacy of journalistic sources, for example, so it's possible that the act of publication itself might be considered a prerequisite to a 1A defense. I hope I'm overthinking this but it does seem to be a bit of a legal hot potato.
https://en.wikipedia.org/wiki/Shield_laws_in_the_United_Stat...