Paul López, Denver's clerk and recorder overseeing elections, has noticed voters have a new concern this year.

"Every single meeting I have, there's somebody that asks the question, 'What can we do if federal agents are at the polls?'" López said.

Federal interference at the polls is against the law. But it is increasingly a scenario López and other voting officials and civil rights groups are planning for and trying to prevent, since Trump administration officials have repeatedly floated the possibility of federal officers at polling locations.

López is part of a coalition that filed a lawsuit last week. Another coalition filed one Friday. Each is aimed at blocking federal officers from the polls under different aspects of federal law. NPR is the first to report on the latest lawsuit, which was brought by civil rights groups and unions.

President Trump, when asked in May about the idea that federal agents could be deployed to polling places, said he would do "anything necessary" to make sure the U.S. has "honest" elections. Earlier this month, Department of Homeland Security Secretary Markwayne Mullin said Immigration and Customs Enforcement agents could serve warrants at polling places. And border czar Tom Homan told Fox News last week that agents would not be "sweeping polling places," but earlier in the year also questioned why anyone would be concerned by such activity.

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