JUDY WOODRUFF:

But first: the dangers of domestic terrorism, extremism and efforts to counter its use of social media.

The attack in Charlottesville underscored just how real this is.

As Miles O'Brien explains, experts who study the psychological and technological underpinnings of extremism say neo-Nazis and Islamic terrorists are cut from the same bitter cloth.

It is this week's Leading Edge and a co-production with PBS' NOVA.