Some voting-rights activists are concerned such encounters could escalate in a tense year that has seen armed militias face off against protestors in the nation’s streets.

Poll watching by partisan observers is a normal feature in U.S. elections that dates back to the 18th century and is subject to various state laws and local rules.

Still, this year’s operation by the Trump campaign is highly unusual, voting rights advocates say, both in its focus on early voting and in its emphasis on finding evidence to support baseless assertions by the president and his supporters that Democrats plan to flood the system with phony mail ballots to steal the election.

In a recruitment video posted on Twitter in September seeking volunteers for this “Army for Trump,” the president’s son, Donald Trump Jr., made the unfounded claim that Democrats plan to “add millions of fraudulent ballots” to rig the results. Trump repeatedly has refused to commit to accepting the outcome of November’s election. During the Sept. 29 presidential debate, he exhorted his supporters to “go into the polls and watch very carefully.”