Drum isn't so sure that Joe Stack was a terrorist. Matt Steinglass differs:
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 thoughts here.