"The left" has been storming Portland, Seattle and many other places instead, for most of 2020, based on the notion that America is filled with white supremacists and the police are systemically racist. Or put another way, because they theorise that white police are involved in an enormous, coast-to-coast conspiracy against black people.

Whether you agree with that belief or not (there was one forlorn WSJ article at the start of all that showing that the data doesn't support it), it is objectively a conspiracy theory in the sense that it posits a conspiracy. And it has led to people repeatedly storming and smashing up not only federal buildings but many others.