On the eve of the New York state primary last month, as Hillary Clinton came closer to the Democratic nomination, Vice President Joe Biden went on TV and defended her husband's 1994 crime bill. Asked in an interview if he felt shame for his role passing a law that has been the subject of so much recent criticism, Biden answered, "Not at all," and boasted of its successes — among them putting "100,000 cops on the street." His remarks sparked a new round of debate over the legacy of the crime bill, which has haunted Clinton ever since she hit the campaign trail with a vow to "end the era of mass incarceration."

A few days later, on April 24, a lesser-known crime law quietly turned 20. The Antiterrorism and Effective Death Penalty Act of 1996 — or AEDPA — was signed by Bill Clinton in the wake of the Oklahoma City bombing. While it has been mostly absent from the recent debates over the crime policies of the '90s, its impact has been no less profound, particularly when it comes to a bedrock constitutional principle: habeas corpus, or the right of people in prison to challenge their detention.