The conference routinely triggers “threatening and ugly emails,” Moore said, often from white supremacists.

So far, none of the emails this year has been directly threatening, said Lt. Dave McCaw of the Madison Police Department, but the department will continue to monitor social media in the days leading up to the conference, as it does prior to any large gathering, he said.

At this point, McCaw said there appears to be no need for off-duty police at the event, though on-duty officers will give the conference extra attention.

Opposition is not uncommon , Moore said. Members of the St. Louis -based Council of Conservative Citizens protested the 2011 conference in Minneapolis. The group did not return phone calls. A recent post on its website called the Madison conference “extremist” and said “Wisconsin taxpayers are being forced to pay for the entire thing.”