Canada has put in place measures that make it more difficult for a dangerous person to acquire a gun, with a focus not so much on banning weapons entirely (the AR-15 is available after undergoing safety training and a screening) as on limiting who can obtain one. In the United States, we lack even universal background checks, and new Harvard research to be published soon found that 40 percent of gun transfers didn’t even involve a background check.

We can’t prevent every gun death any more than we can prevent every car accident, and the challenge is particularly acute with homegrown terrorists like the one in Orlando. But experts estimate that a serious effort to reduce gun violence might reduce the toll by one-third, which would be more than 10,000 lives saved a year.

The Orlando killer would have been legally barred from buying lawn darts, because they were banned as unsafe. He would have been unable to drive a car that didn’t pass a safety inspection or that lacked insurance. He couldn’t have purchased a black water gun without an orange tip — because that would have been too dangerous.

But it’s not too dangerous to allow the sale of an assault rifle without even a background check?

If we’re trying to prevent carnage like that of Orlando, we need to be vigilant not only about infiltration by the Islamic State, and not only about American citizens poisoned into committing acts of terrorism. We also need to be vigilant about National Rifle Association-type extremism that allows guns to be sold without background checks.

It’s staggering that Congress doesn’t see a problem with allowing people on terror watch lists to buy guns: In each of the last three years, more than 200 people on the terror watch list have been allowed to purchase guns. We empower ISIS when we permit acolytes like the Orlando killer, investigated repeatedly as a terrorist threat, to buy a Sig Sauer MCX and a Glock 17 handgun on consecutive days.

A great majority of Muslims are peaceful, and it’s unfair to blame Islam for terrorist attacks like the one in Orlando. But it is important to hold accountable Gulf states like Saudi Arabia that are wellsprings of religious zealotry, intolerance and fanaticism. We should also hold accountable our own political figures who exploit tragic events to sow bigotry. And, yes, that means Donald Trump.

When Trump scapegoats Muslims, that also damages our own security by bolstering the us-versus-them narrative of ISIS. The lesson of history is that extremists on one side invariably empower extremists on the other.

So by all means, Muslims around the world should stand up to their fanatics sowing hatred and intolerance — and we Americans should stand up to our own extremist doing just the same.