The definition of terrorism is (usually) something close to violence carried out by clandestine groups against civilians in the name of some political ideal. The nature of that political ideal is not part of the definition of terrorism. This is why this Newsweek debate is really burning me. Michael Isikoff says that terrorists aligned more with foreign ideologies are more terrorist-y than those aligned with domestic ideologies. Kathy Jones even says that someone should only be labelled a terrorist if they're a foreigner or a member of a foreign group.
This all comes about because people don't want to label the guy who attacked the IRS as a terrorist. Let's see how it matches to the definition:
1) Violence? Yep.
2) Clandestine? Close enough. He's not a member of a standing military that has openly admitted its purpose, therefore, it's clandestine.
3) Civilians? Yes, IRS officials count as civilians. They're not military personnel.
4) Political purpose? Just like the IRS attacker said, he was attacking the government in the support of "liberty."
That's terrorism. End of story.
As usual, Ta-Nahisi Coates has it mostly right. Redefining terrorism to only include outsiders (or those we perceive as outsiders) is to rewrite our own history, to remove blame and moral opprobrium from where it's due.
And despite what some are trying to do, this is not a left-right issue. Yes, the US has a history of right-wing domestic terrorists. However, it's had plenty of left-wing ones as well. William Ayers was once a terrorist, and so was Stack. People threatening abortion doctors are terrorists, and so are those threatening animal research workers.
Stop playing this game, and stop trying to protect those who commit such attacks just because you agree with their ideology.