On Oct. 31, the State Department faces a critical decision in our relations with the Democratic People’s Republic of Korea. The Iran-Russia-North Korea sanctions bill enacted in August included legislation I introduced that requires the secretary of state to decide whether to relist North Korea as a state sponsor of terrorism within 90 days.

Look at the accusations against Pyongyang: the unspeakable treatment of Otto Warmbier; the assassination of a member of the Kim family with chemical weapons on foreign soil; collusion with Iran to develop nuclear weapons and ballistic missiles; cyberattacks on American film companies; support for Syria’s chemical weapons program; arms sales to Hezbollah and Hamas; and attempts to assassinate dissidents in exile. Given this, the decision should be easy. In fact, Americans could be forgiven for wondering why North Korea is not already designated as a sponsor of terrorism.

It used to be — and the story behind the decision to remove that designation nearly 10 years ago is the key to understanding America’s failed assumptions about North Korea, how they led to Pyongyang obtaining its nuclear arsenal, and why the United States needs to reverse its approach and relist Pyongyang immediately.

On Feb. 13, 2007, the State Department signed a deal with North Korea in pursuit of a grand bargain: exchanging Pyongyang’s promise of eventual denuclearization for Washington’s guarantees for full diplomatic recognition. Standing in the way, however, was a decision President Ronald Reagan made nearly 20 years earlier, designating North Korea as a state sponsor of terrorism largely in response to its complicity in a 1987 plane bombing that killed 115 people.