Ron Paul’s fans are furious, according to the headline up on the Drudge Report, because of the stand by the ex-congressman’s son, Senator Paul, on drones. It seems that the Kentucky Republican has no quarrel with the way thermal imaging technology was used to spot one of the suspected bombers of the Boston Marathon hiding under the tarpaulin of a boat in a back yard in Watertown. The senator explained his views in an interview with Neil Cavuto of Fox News. “I’ve never argued against any technology being used when you have an imminent threat, an active crime going on,” Dr. Paul told Mr. Cavuto.

This is evidence that Mr. Paul is emerging as a leader who is both reasonable and principled, a man capable of drawing the kind of distinctions that the best of our legislators, judges, and presidents have always had to draw. It happens that the Supreme Court has made it clear that there are sharp limits on what the authorities can do with thermal imaging. The decision came in a case called Kyllo v. United States, involving a raid by federal agents who had searched Danny Lee Kyllo’s home with a thermal imaging device that saw he was using heat lamps to grow marijuana in his garage.

The Supreme Court would have none of it. It ruled that the Fourth Amendment against unreasonable searches and seizures draws a line around a house that must be “not only firm but also bright.” One of the notable things about Kyllo is that it did not divide the court in the typical right wing, left wing lines. The majority opinion, written by The Great Scalia, spoke for Justices Souter, Thomas, Ginsburg, and Breyer, while the dissenters, who were written up by Justice Stephens, comprised Chief Justice Rehnquist, and Justices O’Connor and Kennedy. It is, in other words, not so easy to do a quick read of the issue ideologically.

This was pointed out today in a column by the libertarian law professor Richard Epstein, to which we were alerted by the Web site Futureofcapitalism.com. Professor Epstein, a sage of New York University, the University of Chicago, and the Hoover Institution, reviews a number of Fourth Amendment cases in light of the drama at Boston. He’s of the view that it “important to think about these procedural issues.” He argues that no one has a “magic formula to determine what counts as reasonable suspicion or probable cause. But that knowledge should not stop the search for clean and workable rules.”

It strikes us as plain on its face that workable rules would include a situation like that involving the younger Tsarnaev brother, who was being pursued by police who had good reason to believe he was armed and dangerous and bent on further crimes. If one mayn’t use a drone to track such a thug with a thermal imaging camera, it’s hard to imagine what one could use a drone for, except delivery of Valentines. Senator Paul was articulate and on point in marking the distinctions in his interview on Fox News, all the more so because of his famous filibuster in demand of an answer to whether a drone could be used to kill an American civilian on American soil. Call it the education of Rand Paul — or the education of his growing band of supporters.