So I think that on definitional grounds, you have to grant that Stack’s suicidal plane attack on the IRS was an act of terrorism. But at the same time, we don’t put it in the same league as attacks by trained agents of Al-Qaeda or the Stern Gang, because it’s not part of an organized campaign of violent intimidation that furthers the aims of a political organization. The Oklahoma City bombing, with its clear links to the militia movement and its explicit (if crazy) ideology, was more like the terrorism we see from Al-Qaeda or the Qassam Brigades. Stack’s act was more like what the Unabomber was up to: the lone act of a disturbed man with no coherent vision of how his desired political change could come about. But, again, we’d all call the Unabomber a terrorist.
My emphasis there, because I think Steinglass is wrong, and the reason why he is wrong gets at the heart of the matter (and, ultimately, reinforces his overarching point as to the ultimate classification of Stack’s attack). We do call the Unabomber a terrorist yes, but I’d say we mean it in the same way that we refer to al Qaeda operatives as terrorists. The reason for that is that the Unabomber wasn’t a one-off lunatic. He committed a series of acts at targets across the country for a long period of time with a specific goal in mind. Yes, that goal was pretty nuts — but no more so than reestablishing the caliphate. It was at least a somewhat coherent goal,* which is something you can’t say about Stack’s scattershot vision.
*Don’t take my word for it; read Chuck Klosterman’s take on the Unabomber manifesto in the closing chapter of Eating the Dinosaur.