America is more vulnerable to assassins than most other democracies, for many reasons. The United States is a less-surveilled society than Britain or France. American police forces are more decentralized than those of most European countries. Above all, the U.S. is vulnerable to this crime because targeted killing typically requires access to a gun—and guns are easier to acquire here than in any comparably developed society. We’ll learn more about when the Alexandria murderer decided on his crime, and whether his weapon was legally acquired. The commonwealth of Virginia certainly did its utmost to ease his way, however, by conferring the legal right to move about with an openly brandished rifle. (The City of Alexandria, though, where the shooting took place, bars the open carry of assault weapons.)

In the wake of this crime, as after the Gabby Giffords attack in 2011, we’ll soon be talking about whether and when political rhetoric goes too far. It’s an important conversation to have, and the fact that the president of the United States is himself the country’s noisiest inciter of political violence does not give license to anyone else to do the same. Precisely because the president has put himself so outside the boundary of political decency, it is vitally important to define and defend that border. President Trump’s delight in violence against his opponents is something to isolate and condemn, not something to condone or emulate.

The good news for American society is that this isolation and condemnation will happen. Across the political spectrum, there is only revulsion. The danger in acts of political violence like this is that some unscrupulous people will use this crime to write a narrative of victimhood to justify their own preparations for political violence in what they will wrongly regard as self-defense. Two days ago, hundreds of heavily armed vigilantes assembled in a Houston park, summoned by a false rumor that the city would remove a statue of Sam Houston. Their intent was to intimidate, but intimidation could under unlucky circumstances easily have tipped into outright violence. That kind of supposedly defensive, actually aggressive, violence has become an even graver risk after today, in an American society that regards personal arsenals to be at least as much of a human right as the rights of free speech and peaceful assembly—and in actual practice, often a more fundamental right.