In the case of the guy who flew his private plane today into the building in Austin which housed the IRS, and did it to get BACK at the IRS (after burning down his house down ...which doesn't make sense but that's another story), the government (or the White House and Homeland Security) has declared it is NOT an act of terrorism.
But not end of story. I ask this in all due respect: if someone targets the government or a particular agency with an act of destruction, resulting in death/injury, and did it willfully (premeditated) ,,, isn't THAT an act of ... terrorism?
... OR can terrorism ONLY be perpetrated by a foreign national?
My answer? Yes, it IS an act of terrorism, regardless of that person's address or homeland. Angry white guys are just as capable of such heinous acts as Arabic-speaking people.
And when you do it in such a calculated way, meaning to do harm, THAT IS TERRORISM!