I think Herndon meant to express the idea that Northam is hopelessly vulnerable and he only accidentally referred to a circular firing squad.
I don't think he is. What's his motivation to resign? If he goes, he's defeated, and no one will care about him anymore. Where will he go? And those who are pressuring him to leave — how can they do anything more? And are they exposing themselves to political injury? Is that accidental invocation of the circular firing squad a little too apt?
Who first thought up that image of the circular firing squad? I'm seeing this in The Nation, "The Circular Firing Squad Isn’t Amusing Anymore/The left is tearing itself apart," by Danny Goldberg in July 2017:
This coming October 9 will mark the 50th anniversary of Che Guevara’s murder. Yet the pathology underlying his famous quip that when the American left is asked to form a firing squad it gets into a circle is as relevant today as a Rachel Maddow response to Kellyanne Conway’s spin du jour.It comes from Che Guevara? I tried to confirm that and could not. And The Nation calls it "famous." Wikiquote has a huge collection of Che Guevara quotes, and the only one about a firing squad — marked as "disputed" — is...
To send men to the firing squad, judicial proof is unnecessary. These procedures are an archaic bourgeois detail. This is a revolution! And a revolutionary must become a cold killing machine motivated by pure hate. We must create the pedagogy of the paredón [execution wall].If you think of the killing as the destruction of a person's career and social standing, that has plenty of resonance in America today. These procedures are an archaic bourgeois detail. Isn't that what's being done to Northam? And shouldn't we feel good then that our firing squads form a circle?

