So is a church, a mosque, or Hindu temple. What makes it special/sacred for certain people is what it stands to represent for them.
For follows of American democracy, it is a sacred place. Despite it being a historical and symbolic monument. The only vandalism that occurred there was 200 years ago when the British army burnt it a few years after it was built.

The rioting riff-raff mob does not understand this although they falsely call themselves fighters of democracy.
The behaviour is no different than a mob of riff-raff went to vandalize Christian cathedrals, ancient mosques or Hindi temples.