Mate of mine wrote a very obviously satirical article about kidnapping the president's daughter (one memorable line was "who knew she could swim like a dolphin?") back in 2008.
He got a visit from the Secret Service. The site that he works for got a visit from the Secret Service. The article doesn't exist in any form anywhere on the internet any more.
The Secret Service will visit anyone who makes what they consider to be a public threat, no matter how outlandish and stupid.
No gray areas. Just don't go there, and you'll be fine. Which makes sense, in a way, as it keeps them from chasing red herrings all over and leaves the investigations for those who are really serious about their intent.
When I was a grad student in Grand Forks, ND, a couple of drunk undergrads decided to go check out a missile silo and see what their tax money was being spent on (I doubt they'd paid a thousand dollars in tax money in their lives, unless you counted liquor, tobacco, and fuel taxes, but that's neither here nor there).
Needless to say, they didn't make it to the perimeter fence before the security QRT swooped in by helo and took those boys off for a very unpleasant weekend of answering questions.
When they got back to campus, they told of their bad weekend, and the AF was safe from idiots for another two or three years...enough time for those to graduate and some other bunch to try.