Photos from Warren's rally Saturday in Storm Lake show 58-year-old Randal Thom, of Lakefield, Minnesota, carrying a sign that read "Keep America Great" — which was a reference to Trump's "Make America Great Again" 2016 campaign slogan.
Police say Thom was involved in an argument with supporters of the Massachusetts senator that turned physical, and that some punches were thrown. There were no injuries and no one else was arrested.
Court records don't list an attorney for Thom and attempts to reach him for comment Monday weren't successful.
Warren's trip to Iowa offered a first glimpse of what she may look like as a candidate for president if she runs in 2020.