The United States has been at war with radical Islamist terrorism for at least 35 years, starting with the November 1979 Iranian seizure of the U.S. Embassy in Tehran and taking of 52 American hostages. President Jimmy Carter, in his State of the Union address two months later, declared the American captives “innocent victims of terrorism.”

For the next two decades, radical Islamist terrorism grew more powerful and more sophisticated. On Sept. 11, 2001, a remarkably sophisticated effort by Islamist terrorists killed nearly...