conspiracy charges are a thing, and they'll only need a few examples of manifestly illegal interference.
it will be quite easy for a prosecutor to charge lots of these people.
it's been done for less, and even if the case is thrown out it can drag on for years and involve jail time before any conviction.
Conspiracy requires an agreement to commit an illegal act, and entering into that agreement must be intentional.
If they could arrest people for what they've been doing, they would have already arrested people. And they have arrested a few here and there for "assault" (things like daring to react when being shoved by an annoyed officer), but the thing that's really pissing DHS off is that the protesters and observers are not breaking the law.