While Mr. Trump insists that he does not have “a racist bone” in his body, his history of making racist remarks says otherwise. After years of suggesting that President Barack Obama had not been born in the United States, Mr. Trump launched his presidential campaign in 2015 by likening Mexican immigrants to criminals and rapists. He recently said that four congresswomen of color should “go back” to the countries from which they came. The list goes on. When the most powerful man in the world uses such toxic rhetoric, we should not be surprised when others mimic him.

Beto O’Rourke, the former congressman from El Paso and a Democratic presidential candidate, recently told me that he is convinced Mr. Trump influenced the attack. Mr. O’Rourke — who along with Senator Elizabeth Warren, another Democratic candidate for the presidency, has said in recent days that Mr. Trump is a “white supremacist” — responded to a tweet from the president by writing: “22 people in my hometown are dead after an act of terror inspired by your racism.” Other leaders and politicians, including Representative Alexandria Ocasio-Cortez, have also lost their patience with Mr. Trump. “I don’t want to hear the question ‘Is this president racist?’ anymore. He is,” Ms. Ocasio-Cortez said recently.

The president’s xenophobia, and that of many of his supporters and enablers, is rooted in a dread that the day is soon coming when they will be a minority in their country . While non-Hispanic whites remain a majority of the population in the United States, in less than 30 years that may no longer be the case, according to projections. This sort of demographic revolution is putting Americans’ tolerance to the test. Most of us welcome an increasingly diverse country, but many, like Mr. Trump, resist the country’s multiethnic, multicultural future. Some react by walking into a store and murdering innocent people.

The most racist Americans who are set on killing minorities are aided by the fact that they can easily obtain assault weapons in this country. I’ve lost count of all the massacres I’ve covered as a journalist. After each shooting — Columbine, Sandy Hook, Las Vegas, Parkland — I thought we might have reached the limit of Americans’ tolerance for such horror. But it wasn’t so. I fear that the killings in El Paso won’t change anything, and that I soon will be back on another flight headed to cover the next massacre. And then another. And another after that.

I have lost hope that the United States will ever pass laws that limit access to firearms. Like many parents around the country, I’ve had difficult conversations with my children in case they find themselves in a situation where someone is shooting at them. “Try to escape, hide or fight,” I tell them. “But don’t stay still. Gunmen have a lot of bullets, but not patience.”