https://en.wikipedia.org/wiki/United_States_federal_executiv...
It's a real cop-out to say his hands were tied. He had wide latitude and authority to implement changes within the executive branch.
Obama was in charge of the entire federal executive branch. The problem at the core of anti-police protests is not the FBI and not any other federal branch (okay, a bit the DEA/ICE), it is local police and sheriffs!
To make it worse, a large part of the blame lies on police unions, e.g. in Minneapolis, whose leaders are hard authoritarian/right-wing and use all powers they have including staging expensive and often successful legal battles to keep "bad apple" cops in the service instead of holding them accountable.
For some reason CGP Grey's video called The Rules for Rulers was recommended to me recently by The Algorithm. It sort of clarified in my mind all the vague ideas I'd absorbed from countless online and in-person conversations. Basically, even a dictator has to have the support of the keys to power. We can speculate that a president's hands were tied by one of those key groups. We can also speculate that another president has different key groups, and might be more willing, with the consent of core key groups, to reduce their numbers in ways not previously/recently considered an option.