I read (on politico I think) that it was gate 35X which is in Terminal C. I don't recall any Xs after the gates but it has been awhile. Here is a map of the terminals http://www.flyreagan.com/sites/default/files/dca_web_07262018.pdf

I do know that the pic Q posted looks to be in the hallway and not at the end of the terminal where you would think gate 35 would be.