The marches have attracted a mixed crowd of civil rights activists and people who oppose vaccinations, as well as neo-Nazis and members of the far-right.
Cantwell, 39, is also expected to face a civil trial for his role in the white supremacist violence that engulfed Charlottesville, Virginia, in 2017.
Authorities searched the home of Andrew Richard Casarez, aka white supremacist “Vic Mackey,” and confiscated a gun, an official said.
Cantwell has harassed and threatened people for years since participating in 2017's deadly white supremacist rally in Charlottesville, Virginia.
Federal prosecutors asked to detain three members of the violent extremist group The Base, arguing that they had plotted violence to spark a civil war.
The men are all alleged members of The Base, a white supremacist group that hopes to start a race war.
The Monday gathering in Virginia already has prompted the state's governor to enact emergency measures to thwart violence.
The 17-year-old is the youngest person to be convicted of planning a terror attack in the United Kingdom.
The video giant declined to remove an Atomwaffen Division video when it was first reported last week.
Jeffrey Clark pleaded guilty to a gun charge in July and served nearly 10 months in custody.