In 2016, a bomb exploded in Chelsea on the west side of Manhattan. The bomb—timed to inflict maximum damage by being set on a busy Saturday night—injured 31 people and caused serious property damage.

The following day, New York City mayor Bill de Blasio declined to label the bombing "terrorism." He was asked directly about this—was it terror?—and answered, “Here is what we know: It was intentional, it was a violent act, it was certainly a criminal act, it was a bombing — that’s what we know . . To understand there were any specific motivations, political motivations, any connection to an organization — that’s what we don’t know.”

CNN defended de Blasio's reticence. One of its national security analysts pointed out at the time that, "When investigators and politicians are unwilling to say it's terrorism, it's not because they're 'PC' or anything like that, it's just that the investigation has to unfold naturally." Fair enough.

Fast forward two years. On Wednesday, CNN evacuated its New York facilities after a suspicious package was found. Yet Mr. de Blasio emerged with guns blazing: Within hours, he had labeled the incident an "act of terror."

For those keeping score at home: An actual bomb explodes, injuring dozens. That's not terror. But a "suspicious package," that may or may not contain an explosive device, is sent to CNN: That's definitely terrorism. Unless Mr. de Blasio knows the "specific motivations" of who sent the package—and if so, he should probably call the FBI immediately—it would appear his definition of terrorism has changed.