See Slate’s complete coverage of the Gabrielle Giffords shooting and arrest of Jared Lee Loughner.

Of course it was political.

In the Fort Hood shootings of November 2009, the right was quick to link Nidal Malik Hasan to terrorism, while the left insisted he was merely deranged. The reactions to the attempted assassination of Rep. Gabrielle Giffords and the murder of six others this weekend offered a mirror image: Many on the left blamed right-wing political extremism, while conservatives insisted that Jared Loughner, the alleged killer, was a lone lunatic, without political motivation.

If a whiff of political opportunism clings to both these sets of reactions, it’s because the categories that we use to explain political violence draw bright lines where none really exist. Throughout history, political assassins—even the most clearly unhinged among them—have possessed political motives. That doesn’t mean that Tea Party-style rhetoric incited Loughner. But his choice of targets—an officeholder, not a post office or a mall—can’t be dismissed as arbitrary. The problem lies in the artificial distinction we routinely draw between political and psychological motives.

Before the rise of liberal democratic norms, when violence was a common and viable way to overthrow political regimes, there was seldom doubt that an attack on an office-holder was political in nature. The insanity defense became plausible with the M’Naghten Case of 1843, in Britain, in which Daniel M’Naghten, trying to kill Prime Minister Robert Peel, instead murdered Peel’s secretary. The House of Lords then developed rules for accepting claims of insanity. They allowed the defense in instances where mental disability meant that the accused did not know “the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong.”

Over time, these guidelines and the ideas that informed them made their way into American law. They came to shape public discussions about assassinations as well. When John Wilkes Booth, a vehement defender of the Confederacy, murdered Abraham Lincoln, virtually everyone agreed that he acted for political reasons. He was part of ring that also targeted Vice President Andrew Johnson and Secretary of State William Seward. Although historians have debated the precise nature of Booth’s motives, few have doubted that he did so to aid or redeem the Confederate cause.

In the late 19th century, however, psychiatry began influencing criminology. The new approach to crime and the law created more opportunities for insanity defenses—in not only the courtroom, but also the court of public opinion. What began to emerge was today’s sharp distinction between political assassination (which was deemed “rational” and the expression of an ideology) and derangement (the condition of an isolated individual).

When Charles Guiteau shot James A. Garfield in July 1881, his sanity was a central point of contention. It was obvious that Guiteau targeted Garfield for political reasons. Deeply invested in the outcome of the 1880 presidential election, he grandiosely expected to be recognized for a pro-Garfield pamphlet he had written, even though he had no significant connection to the campaign. That he wasn’t appointed minister to Austria or some other office prompted him to beseech the White House and the State Department repeatedly for a position, to no avail—leading eventually to his decision to kill Garfield.

Yet Guiteau was also plainly delusional, quite possibly a paranoid schizophrenic. He claimed that God instructed him to “remove” the president. Over his objections his defense team pressed the insanity defense, calling doctors as witnesses. But despite Guiteau’s bizarre behavior at his trial, which included blurting out insults to the judge and to his own lawyers, the argument failed.

Political motivations were also apparent in the case of Leon Czolgosz, who fatally shot William McKinley in September 1901. A consumer of anarchist literature, Czolgosz claimed to have been inspired by a speech by the famous radical Emma Goldman. Goldman was subsequently arrested, but she disavowed any support for assassination and, after being cleared of any connection to Czolgosz, was released. Nonetheless, many anarchists held to the principle that violence was a legitimate means of change; Goldman’s lover Alexander Berkman served 14 years in jail for trying to murder the industrialist Henry Clay Frick. In short, it was seen as entirely possible to offer a “rational” motive for political violence.

Gabrielle Giffords’ Doctors Give an Update on Her Condition

But did Czolgosz’s attack on McKinley fit that description? As sometime Slate contributor Eric Rauchway notes in Murdering McKinley, the defense tried to argue otherwise, likening McKinley’s murder to death by railroad accident—a freak occurrence, in effect, not a reason to implicate society or question its social arrangements. To find Czolgosz not guilty by insanity would, his lawyer told the jury, “aid in uplifting a great cloud off from the hearts and minds of the people of this country and of the world.” By contrast, Theodore Roosevelt, the new president, called the killer an ordinary criminal. The jury agreed, sentencing Czolgosz to death.

In the 20th century, defendants invoked the insanity defense with growing frequency, and in a widening set of circumstances. Its spread helped solidify the artificial distinction between political and psychological motives. Killers had to be put into one box or the other. An assassin might be judged as sound of mind and possessed of extreme ideological views that produced calculated violence. Or he might be judged as mentally unstable, with his political rantings waved off as simply the incoherent expressions of a malfunctioning brain. The two categories were usually treated as mutually exclusive.

In fact, those who try to kill politicians may well be both ideologically motivated and psychologically abnormal. Occasionally, as with John Hinckley’s attempt on Ronald Reagan’s life, the choice of a target may have more to do with his celebrity than his ideology. But more common are cases like that of Sirhan Sirhan, the Palestinian assassin of Robert F. Kennedy. (In 1968, when the murder occurred, the newspapers labeled him Jordanian because Jordan then laid claim to the land of his birth.) Sirhan wanted to kill Kennedy because of his support for the state of Israel, especially following the 1967 Six-Day War. At the same time, he also underwent brain X-rays and psychiatric tests to help establish grounds for an insanity plea. One line of defense even attributed Sirhan’s derangement to having been thrown from a horse two years earlier. Again, the argument failed; Sirhan, 66, remains in a California prison.

Much has been made in the last few days of the power of symbols (bull’s-eyes, cross-hairs), martial rhetoric, the hyperbole of words like tyranny. But the most important symbols in all of this are politicians themselves. By the nature of their position, candidates and officeholders excite powerful feelings among ordinary citizens that may not correlate closely with their actual deeds. This is true of presidents especially, whom we tend to regard, from childhood, as the personification of the nation itself. (When presidents die, reports of psychosomatic illness tend to rise). Whether medically composed or deranged, whether legally sane or insane, assassins train their consuming energies and hatreds on politicians not for purely arbitrary reasons but because politics matters to them—usually far out of proportion to the actual power of their victims.

Like Slate on Facebook. Follow us on Twitter.