Hundreds of thousands of protesters representing 28 groups have begun to descend on Washington, D.C., as Donald Trump’s Jan. 20 presidential inauguration draws near. The National Park Service, which oversees much of the inaugural festivities, estimates that as many as 350,000 demonstrators could take to the streets. As is often the case with such estimates, the actual number of protesters is likely to be much smaller.
This inauguration will provide an opportunity for most demonstrators to channel their energy toward a single cause -- opposing Trump. In some locations, they may be protesting near pro-Trump groups. This could increase the drama, but a significant police presence is likely to forestall significant violence. Most of the groups planning demonstrations are associated with established protest or political movements. However, agitators could use the opportunity to incite violence despite the massive security presence in the city. And hanging over the entire event is the...