Which brings us to another consideration: As with the case of the perpetrators of the homicidal violence that plagues so many American cities, many terrorists and other perpetrators of mass killings are people who are hardly unknown to our law-enforcement authorities. Mateen was on the federal radar. Adam Lanza’s mental-health problems were no secret in his community. More than 90 percent of those who commit murders in New York City have prior criminal histories. The Fort Hood shooter was in contact with Anwar al-Awlaki, and that fact was known to the FBI. These killers do not come out of nowhere.

The habitual Democratic response to these episodes is to demand that we restrict the legal rights of people who have not been charged with, much less convicted of, a crime, which is constitutionally, legally, morally, and politically impossible. Beyond that, we get speeches that sound like they come from party functionaries in some cartoon version of a 1930s totalitarian state: Mrs. Clinton promises that we shall “redouble our efforts!” against terrorism, while President Obama vows that we shall “spare no effort!” in our investigation of this atrocity. One half expects them to promise that the wheat harvest will double under the five-year plan unless the wreckers and hoarders sabotage our program.

The fact is that we are not redoubling any efforts, not where it could really count: screening people who enter the country legally and preventing illegal entries. Nor is it the case that we are not sparing any effort: We have a national-security apparatus perfectly comfortable monitoring basically all electronic communication, but we can’t put a tail on a guy the FBI twice had reason to suspect of being involved in terrorism?

The fact is, the federal government does not take this sort of thing very seriously at all.