Recently there was the attempt to kidnap the Michigan's governor and the cell that was planning an attack on a power plant.

Both stopped by intelligence services, but that doesn't stop them being data points for people being extremists.

Not saying there is a guarantee this was people with the same objectives, but it seems like a plausible theory. I wouldn't make strong assertions as though it was fact, but I also wouldn't act like there hasn't been a trend recently.