Is the United States government trying to kill Moammar Gaddafi? Not officially. For the record, the United States issupporting a NATO mission to protect civilians from Gaddafi’s forces. NATO jets are bombing Gaddafi’s command and control centers. If Gaddafi dies, it may be from a French bomb. But the United States pays more than a fifth of NATO’s costs and provides at least some of the high-tech intelligence used in bombing runs. If Gaddafi is killed in one of those raids, America will have a hard time convincing the world that Gaddafi was not the target.

President Obama would never be so crude as to say “dead or alive,” and he has told Congress that he has no plans to use the American military to assassinate Gaddafi. But by making clear that he wants regime change and signing off on the NATO strikes, he is, however indirectly, taking on responsibility for attempting to kill a head of state.

That is no small step for an American president. Yet there has been little discussion of assassination in Congress or in the media. There should be more. It is worth looking at the history of assassinations and asking whether the president and Congress really want the United States to support efforts to kill heads of state, even wicked ones such as Gaddafi. Aside from the moral questions, assassination invites instability and blowback.

In the West, assassination was a fairly common tool in international relations until the late 18th century. Then nation-states pulled back. The rules of war recognized that while states could make war on each other, heads of state should be protected. In 1789, Thomas Jefferson wrote to James Madison, “Assassination, poison, perjury. . . . All of these were legitimate principles in the dark ages which intervened between ancient and modern civilizations, but exploded and [were] held in just horror in the eighteenth century.” In 1938, the British government rejected a proposal by the British military attache in Berlin to assassinate Adolf Hitler on the grounds that it was “unsportsmanlike.” As late as 1944, the British government was divided over a plan by the British Special Operations Executive to liquidate the Nazi leader.

As Ward Thomas, a professor at the College of the Holy Cross, writes in “The Ethics of Destruction,” the norm against assassination gradually loosened after World War II. It was recognized that heads of state could be terrorists and war criminals — if not human monsters. In 1986, after Gaddafi was held responsible for a terrorist attack that killed American servicemen in a nightclub in Berlin, the United States bombed Gaddafi’s tent in Libya, killing some of his relatives. In the opening blow of the 2003 Iraq war, American bombers attempted to kill Saddam Hussein, believing, thanks to faulty intelligence, that he was at a location outside Baghdad. The U.S. executive order banning assassinations, adopted after earlier CIA plots against Cuba’s Fidel Castro and others were exposed in 1975, does not apply in wartime. “The laws of war clearly permit states to use lethal force against the chain of command of military forces who are engaged in armed conflict,” says former CIA general counsel Jeffrey H. Smith. “But we need to be very careful how we use that force, to make sure we are not setting a dangerous precedent.”

As was much discussed last week, technology such as “smart” bombs and aerial drones allows the United States to zero in on individuals. Drones are effective and, for the most part, reduce civilian casualties. But they are turning a crude bomb into a sniper’s rifle. America is far ahead in the race to build better drones, making them small and in the future probably even tiny, like sinister birds and insects. But other nations (and terrorists) will catch up. I can’t help thinking of that not-so-distant day when they may use such weapons; after all, Gaddafi blew up an American airliner after U.S. warplanes bombed his tent in 1986.

It has never been clear whether President Dwight Eisenhower gave the CIA the go-ahead to try to assassinate Castro and Congo strongman Patrice Lumumba in 1960. But Ike surely had it right when he scolded a staffer for making a joke about “bumping off” Lumumba. “That is beyond the pale,” Eisenhower said, according to his staff secretary, Andrew Goodpaster. “We will not discuss such things. Once you start that kind of business, there is no telling where it will end.”

Evan Thomas is an author and professor of journalism at Princeton University.