The only people who can get rid of the corrupt leaders are the Indians themselves. The federal government has absolutely no say in the matter. Just try sticking your nose into tribal business and see what happens.
The BIA and the feds were in bed with the corrupt tribal leaders for decades and looked the other way and often even supported them. Basically, it would take the feds preventing intimidation and corruption leading up to elections - when tribal leaders control your allotment of benefits and their authoritarianism prevents job creation on the rez, you're screwed.