Plotting a terrorist attack is absolutely a crime in America. I used to believe there was no such thing as a stupid question yet today I am reevaluating this belief.
A couple of points on this arrest:
This is the second association of coast guard members to white nationalism. What’s up with that?
And, big shout out to the Coast Guard on whole for recognizing, reporting and investigating their own. These things do not always get the internal scrutiny they deserve but the coast guard took this seriously and did a nice job.
That's the Crux of it. From reading the OP, I don't think it went that far, but am honestly unaware where the 1st amendment crosses into criminality for plotting an attack.
Gun nuts are quick to jump on the feds for not acting on suspects, but at what point do we put a person's 1st amendment aside when doing so?