Yglesias contemplates the difference:
What’s interesting in particular about the militia mindset, however, is that its narrative sources are very different from those of left-wing radicalism. People who believe in violent revolution and the murder of American soldiers and policemen generally, if on the left, appeal to basically anti-patriotic attitudes. Which is about what you would expect from advocates of the violent overthrow of the established political order. But the militia crowd exhibits much more the attitudes one would expect from a coup leadera Franco or a Pinochet who’s actually appealing to the concepts of patriotism and nationalism as justification for violent revolution.