DC is not a state, it’s a district under federal control. There is a mayor and a police department, but responsibilities that would normally fall to a state-level government are handled federally.
This is a contentious issue in the US right now, because it means that the residents do not have representation in the house and senate.
Further, the insurrectionists were definitely armed, at least five guns were seized from among those arrested.
https://ktla.com/news/nationworld/13-arrested-5-weapons-reco...
From Merriam-Webster
Armed protestors invaded the Capitol intent on disrupting the government from certifying an election. This was quite literally an insurrection.
In the case of Washington, DC they are not. The mayor has a normal municipal police force and the president has control over the equivalent of the state-level force, which would usually be called for such an incident. The Capitol specifically also has another force, independent from the municipal police, which is federally controlled.
There are numerous reports Trump explicitly refused to allow the National Guard to respond; governors of two adjacent states mobilized their state forces instead, and eventually Pence also mobilized the DC guard, which it's not really clear he had the authority to do (or if he does, also the authority to issue orders contravening Trump's refusal).
He can certainly influece it, but did he? If not, who is responsible for the lack of defensive preparations, the local police? The FBI?