Here is some more info:
https://www.freep.com/story/news/local/michigan/2020/10/08/governor-gretchen-whitmer-kidnap-plot-militia/5921409002/
https://www.nbcnews.com/news/us-news/six-men-charged-alleged-plot-kidnap-michigan-gov-gretchen-whitmer-n1242622
From the NBC article:
“Based on court documents, the FBI was well aware of the activities of the men charged Thursday and there does not seem to have been an imminent threat posed to Gov. Whitmer, a Democrat.”