I could not think of something more that America needs. The government accountability office publishers reports all the time about government waste and malfeasance, but it is consistently, dare I say, pointedly, ignored. Having a separate independent agency, cast with investigating and prosecuting crime and criminals within the government itself would be amazing.
Same with congress.
I'm sure it would end badly, but sometimes I fantasize about the U.S. citizens having a LEO that actively investigates / prosecutes government officials who violate the constitution.