The Capitol was in the midst of construction during the Civil War. It was used as a hospital, the grounds as an encampment. No military movement by Confederacy against DC...they were busy defending what they considered their homes against the Invasion.

I lived through the Vietnam peace movement , the Capitol bombing and the onslaught of demonstrators who forced their way into every corner of the office buildings and the Capitol. They attacked people and art. They were filthy and left garbage wherever they roamed.