And the only thing that can stop them is from the inside: a meaningful mass movement by Muslim governments, clergymen and citizens to delegitimize this behavior. It takes a village and only stops when the village clearly says, “No more!” And that has not happened at the scale and consistency it needs to happen.

Finally, in an age when individuals can become super-empowered, we need to ensure our government has all the surveillance powers it needs — under appropriate judicial review — to monitor and arrest violent extremists of all stripes. The bad guys now have too many tools to elude detection.

Obama closed his speech at Hiroshima with words that could easily have been said of Orlando: “Those who died, they are like us. … They do not want more war. They would rather that the wonders of science be focused on improving life and not eliminating it. When the choices made by nations, when the choices made by leaders, reflect this simple wisdom, then the lesson of Hiroshima is done.”

We need to make choices appropriate for our age when technology can so amplify the power of one. We need common-sense gun laws, common-sense gender equality and religious pluralism and common-sense privacy laws.

But that takes common-sense leaders, not ones who think the complexities of this age can be bombed away, walled away, willed away or insulted away. Stop for a moment and reflect on what this week would have been like had Donald Trump been president — the carpet-bombing he’d have ordered in the Middle East, the fear and isolation his Muslim ban would have engendered in every Muslim-American, the joy that ISIS would have taken from being at war with all of America, the license this would have given to crazies in our own society to firebomb a mosque. And the backlash that would engender among Muslims around the world, the most radical of whom would be firebombing our embassies. When America goes nuts, the world goes nuts.

I don’t agree with Obama on all aspects of this issue, but the guy is thinking deeply and acting responsibly. Trump is shooting from the hip, spraying insults 360 degrees, telling lies, stoking fears and making threats that many in our military and the F.B.I. would refuse to implement. If you Republican senators and congressmen support Trump for president, he will own you — and you will own everything he does.