Citizen Volunteers in Polling Places

Are American citizens without any special status permitted to go to polling stations to "guard against fraud?"

I read in the New York Times (https://www.nytimes.com/2020/09/25/opinion/sunday/trump-election-supreme-court.html?searchResultPosition=6) :

"That was when Trump supporters descended on a polling location in Fairfax, Va., and sought to disrupt early voting there by forming a line that voters had to circumvent and chanting, “Four more years!”

This was no rogue group. This was no random occurrence. This was an omen — and a harrowing one at that.

Republicans are planning to have tens of thousands of volunteers fan out to voting places in key states, ostensibly to guard against fraud but effectively to create a climate of menace. Trump has not just blessed but also encouraged this. On Fox News last month, he bragged to Sean Hannity about all the “sheriffs” and “law enforcement” who would monitor the polls on his behalf. At a rally in North Carolina, he told supporters: “Be poll watchers when you go there. Watch all the thieving and stealing and robbing they do.”