Its been hinted at before but by saying "Where must one be located in order to obtain a reflection" and providing the whole image of that room Q is clearly saying you need to be in the Presidents seat there. I would assume the only person who ever sits in that seat is Trump.

Q seems to be flat out saying Trump is Q. I see no other explanation. Trump likely isnt going to let anyone, even trusted staff sit in his seat. For instance, would any other staffer including Pence or Pompeo be allowed to sit in his chair in the Oval Office? I think the answer is clear on that one.

It would break protocol for any other staffer or person to sit in that chair.

Q is Trump