chapotraphouse

have enough tools to make their job idiot proof

This is really it at the federal level, especially with investigations into political groups. You have tons of resources and access to information, and the ongoing nature of what you're investigating means you can take however much time you need to build your case (contrast this with, say, solving a murder that has already been committed). The DOJ works with you from the jump to make sure you're getting what you need for court. When you get to court, you're dealing with lengthy federal sentences so your defendants have tons of incentives to make a deal.

If you really fuck up and there's a newsworthy crime you theoretically could have prevented, that's spun as you needing more power/resources next time around.