Running instances costs money & labor, and I predict that many instance admins will be happy to accept various forms of assistance, and the CIA/FBI/etc-backed organizations will be happy to help. The assistance might be just money, which comes with strings attached such as simply having the ear of the admins. The assistance might be “moderation tools,” to save labor efforts.
I think the instances that choose to federate with corporate social media (which are already captured by feds) will probably be the easiest to gain control of. If you’ve been following the corpo federation discourse, you might have noticed that the instances with the largest user bases tend to be the most interested in federating with the corpo social media.