On Election Day, the U.S. Attorney General must deploy federal law-enforcement officers, in identifying attire, to threatened polling places to PROTECT VOTERS against INTIMIDATION by perhaps-armed activists.
Ignoring that election operations have long-standing oversight by poll-watchers from all parties, presidential candidate Donald Trump has repeatedly urged his followers to "monitor" selected polling places - "you know what I mean!" - to functionally intimidate voters likely to oppose Trump's candidacy. Especially in Latino, black and "liberal" areas. He has even mentioned hiring off-duty police officers to thus act falsely under color of armed authority for partisan intimidation.
Such voter intimidation WAS effective - by Brown Shirts in 1930's Germany.