I have a friend who is a retired Scotland Yard detective and he has an interesting take on the US war on drugs: we effectively put hundreds of billions of dolars a year into the hands of organized crime, and the possibility that there are payoffs to the US Congress to keep this money flow going is a real possibility.
When that kind of money is involved, it's impossible not to have affected the highest levels of the legislature, executive, and judiciary. I believe there have already been documented cases of folks with dubious affiliations funneling money to various PACs. That has to be just the tip of the iceberg.