I think the Keystone is the Presidency…..
In this case Trump but really it is just the office of the Presidency.
The people involved in this Q movement needed to put one of their people into the office of the Presidency or else they would have to attempt an old fashioned bloody military coup.
Which would of gotten even people that should of been allies of the coup to attack it. It have any success they needed the Presidency so they can cover everything they are doing with the trappings of legality.
Thus I think the office of the Presidency is the Keystone. Winning the office has allowed all the long planned moves to start.