That’s just it: Even if Trump were at the WH Pence would still have authority to call out the NG to the Capitol if he were at the Capitol. Pelosi would have the authority if she were the highest federal official on site at the Capitol.
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I suspect you are correct.
At the State Level, the Governors can call up the National Guard. At least for now D.C. isn’t a state so you would need to dig into National Guard laws, rules, regulations to see who is actually has the necessary authority to call them up.
It’s pretty straightforward. I don’t have the exact cites handy, but there is a DC statute naming the President as the Commander in Chief of the DC Guard, and there is a 1969 Executive Order signed by Nixon delegating control of the Guard to SecDef.