The Wrath of the Killdozer (2009)
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Its pretty obvious that Marvin Heemeyer was completely insane, not some kind of reasonable person pushed over the edge by an evil government.
Also he doesn't really fit the definition of a domestic terrorist, he never seemed to be pushing a narative and didn't actually kill anyone.
Sure, but the intention was clearly there. He had guns inside, had shot them from a gun port in the chassis, destroyed structures that were occupied until they were hastily evacuated, and had people's names on his kill list.