Minutes before a shooter opened fire in an El Paso, Texas, Walmart on Saturday, he allegedly posted a racist screed online, declaring his motive to fight a "Hispanic invasion of Texas."

Authorities believe he acted alone, but in an age of online extremism, what does that mean?

National security expert Juliette Kayyem told Boston Public Radio on Wednesday she believes the term "lone wolf" shouldn't be used to describe the men who commit acts of terror after being emboldened by rhetoric on the internet and from the White House.

"It disentangles the ideology from our responsibility to combat it," Kayyem said. "We are in a time in which white supremacy, white-supremacist terrorism, is on the rise. The FBI views it as the greatest terrorism threat. It's not ISIS, it's not immigrants, it's this."

FBI officials said recently the number of domestic terrorism suspects the bureau has arrested has risen, and now roughly matches international terrorist threats.

In an op-ed published in TheWashington Post on Sunday, Kayyem argues that white-supremacist terror is fed by three creeds: mission, kinship and acceptance.

Young white people today are the last generation of Americans born when white births outnumbered those of nonwhites, Kayyem writes, and those who adopt this strain of white supremacy see this as a "great replacement" that threatens their very existence.

She writes that they find kinship in online platforms, which allow 21st-century white supremacists to gather — not unlike Klansmen gathering in the woods.

"This idea that they now have acceptance at the highest levels of government, this is what's different today," she told Boston Public Radio. "You have to think about what's happening as a network of activities that's promoting this violence, and the acceptance these guys are getting, which we know from their manifestos, is the language of Donald Trump. The wink and the nod, the flirtation, the come hither, in terms of displacement and 'the other' and how he describes Hispanics and Mexicans and African Americans and communities of minorities. That language is mirrored."

While Trump's inflammatory rhetoric does not bear the entire burden of white-supremacist violence, she argues, his language is a contributing factor.

"The Trump administration, Fox News, and others, do not shame white supremacy, so it gets acceptance," Kayyem said. "The use of the bully pulpit by Trump has contributed to the greatest threat of United States terrorism today. ... I'm just done going around this issue. The president is contributing to a white supremacist terrorism that is the greatest terrorist threat to American citizens today, more than any other terrorist or racially or politically motivated violence is."

Kayyem is a CNND analyst, former assistant secretary at the Department of Homeland Security and faculty chair of the homeland security program at Harvard University’s Kennedy School of Government.