DC is really strict on gun laws, even after Heller, which tossed out some of the strictest gun regulations. So if there's anywhere this would be illegal, it would probably be DC. But it sounds like the real issue might be something hard to get a read on beyond what's contained in the Post article itself.
The article suggests an air of menace in the use of the gun -- and that's not terribly surprising if the situation was an inherently confrontational one (Armey was ordering people out of the office) and Armey associate came with a holstered handgun. But a lot of that is going to come down to perceptions. And the Post reporter might have played some of the gun angle up for effect.
But using a firearm to intimidate someone can be assault.
A one other thought about DC in general. Post-9/11, Capitol Hill and Northwest DC's business offices have a lot of very elaborate if sort of flimsy building security. I'd be sort of surprised if you could just walk right into most buildings carrying a firearm, without anyone at least asking what was up. But Armey's a big wheel and was a tenant, so perhaps that wouldn't apply. So who knows?
So for those of you familiar with firearms law, particularly in DC, how does this strike you?
Late Update: A reader flagged to me the relevant DC firearms law, which I believe is post-Heller, since it's still listed on the DC website. Item V, a reads: "No person shall carry within the District of Columbia either openly or concealed on or about their person, a pistol, or any deadly or dangerous weapon capable of being so concealed."
That sounds pretty clear. You can't walk around DC with a handgun. But there are four explicit exceptions -- in home, for "lawful recreational purposes", at your place of business or when it is "being transported for a lawful purpose as expressly authorized by District or federal statute and in accordance with the requirements of that statute."
This was arguably Armey's 'place of business', after all that was sort of what was in dispute in the whole controversy. But the law seems to envision having firearms in the office for protection, not to settle disputes over who controls the organization. Again, we need to come back to the vague and off the record descriptions in the Post article itself. There are too many questions, factual and legal, to be able say anything with certainty about whether DC firearms law was broken. But, as a general matter, it seems clear that you can't walk around DC with a holstered handgun.