“Before a standing army can rule, the people must be disarmed, as they are in almost every country in Europe. The supreme power in America cannot enforce unjust laws by the sword; because the whole body of the people are armed, and constitute a force superior to any band of regular troops.”
Noah Webster, An Examination of the Leading Principles of the Federal Constitution , October 10, 1787
The shooter was a Bernie Sanders campaign volunteer. He callled for Democratic Socialism - just like Ocasio-Cortez. He was deeply invested in liberal politics and hated Donald Trump and frequently wrote to Democrat senators to cajole and advise them. All his friends say he was a progressive liberal.
He said nothing out of line with Democratic party principles and he always called on Democrats to push his agendas and beliefs. All his acquaintences would have labelled him so as they describe him.