Note MI has the same SAPs as NSA, CIA etc as designated post 9-11.

Why is this relevant?

Who can be held hostage and controlled?

CIA thinks its foreign offshore assets are strong enough to defend against the US executive (not accounting for military use on domestic soil).

Why does the Constitution explicitly grant this authority to the President and what is it to prevent?

They knew our agencies would grow in power so much so they could/can hold the executive hostage or engage with bad actors.

Trump nominated someone new to direct every agency but one. He controls the top.