In El Paso, Dayton and Chicago, a weekend of horrific gun violence seemed on the surface to be another spasm of disconnected mayhem, people taking the lives of others almost at random. But on closer examination, the attacks served to illustrate how America’s lone-wolf shooters aren’t really alone.

Whether the proximate cause was political or personal, whether it grew out of ideological indoctrination, mental illness or some toxic blend of factors that left shooters isolated and damaged, each attack demonstrated a troubling disorder festering in modern America.

[How do you stop these people?’: Trump’s anti-immigrant rhetoric looms over El Paso massacre]

The 21-year-old man who allegedly murdered 20 people doing their Saturday shopping in El Paso appears to have taken pains to post a manifesto that leaned heavily on the virulently anti-immigrant rhetoric that inspired recent mass shootings in New Zealand and California, authorities said — though they were still working to confirm its authenticity.

The suspect, Patrick Crusius, did not appear to be part of any organized group, but the four-page screed posted minutes before he opened fire parroted the extreme white supremacist ideology known as “the great replacement” — the idea that newcomers are taking the jobs of white Christians in the United States and other Western nations.

The alleged killer of nine people in Dayton, Connor Betts, was a 24-year-old Chipotle worker and community college student driven by personal grievance rather than political ideology, authorities said. Betts, who was killed by police, shot his own sister among his victims.