Thousands of Juggalos are expected to travel from all over the country for Saturday's march, meeting outside the Lincoln Memorial from 1pm.
Pennsylvania is one of four states that has designated Juggalos as members of a hybrid gang.
The protesters listened to a series of speakers and musicians amid clouds of marijuana smoke.
Police say they are ready for all of the activity.
Saturday was a busy day in the nation's capital. That demonstration will focus on Russian interference in the 2016 election. She said she had been profiled by police in OH because of the gang designation.
The pro-Trump crowd, meanwhile, were assembled for a rally created to give the president a signal of their support as Trump struggles through the early months of his first term.
The Washington Mall will hold what organizers are calling "The Mother of All Rallies" in support of President Donald Trump.
Kicking off a Saturday of diverse demonstrations, about two dozen protesters gathered in Lafayette Square, a park just across Pennsylvania Avenue from the White House, to demand that Trump take strong action against Russian leader Vladimir Putin in retaliation for Moscow's interference in the 2016 USA election.
In 2011, juggalos, the name fans of the rap group are known as, were branded as a "loosely organized hybrid gang" by the Federal Bureau of Investigation.
Unlike the annual bacchanalia and music festival anchored by the Detroit-based hip-hop duo Insane Clown Posse known as the Gathering, today the iconic - and some say potentially unsafe - fans of the band will be headed to the National Mall in Washington, D.C. on Saturday afternoon and evening to make a political point of protest.
The controversy stems from the FBI's 2011 Gang Threat Assessment report, in which law enforcement officials listed the Juggalos - the adopted name of ICP's rabid, paint-faced fan base - as a "loosely organized hybrid gang", citing sporadic small-time criminal behavior but a larger potential for some subsets engaging in "more gang-like activity".
The Mother of All Rallies Patriots Unification Gathering will take place at the National Mall near the Washington Monument from 10 a.m. ET to 5 p.m. ET.
On Saturday, downtown Washington, D.C., was home to three prominent demonstrations that some feared might combine violently but instead stayed largely separate and peaceful, with modest attendance.
The organizers of the pro-Trump rally had said that was their goal - to speak in favor of the President amicably, without a hint of the hatred and violence that gripped Charlottesville, Virginia, last month when white supremacists marched in protest of the removal of a statue of Confederate Gen. Robert E. Lee from a city park.
Georgia Power warns of potential Irma scams
Officials are holding daily calls with those facilities to make sure they have everything they need to care for their residents. Most of the remaining outages were in Florida Power & Light's service area in the southern and eastern parts of the state.
Davis Cup: France, Serbia level at 1-1 on day one
The other singles match, if needed, is scheduled to pit Belgium's Steve Darcis against John Millman. Arthur de Greef and Ruben Bemelmans will team up against John Peers and Jordan Thompson in doubles.