How much does any President learn about MJ12, and what does the smarmy group that calls itself the Congress of the United States know? Next to nothing, and this more by rumor and innuendo. MJ12 limits its membership on a need-to-know basis, which should not surprise anyone as it is run by military intelligence units. Why would the current Congress or its current President need to know anything when they are just passing through? Of course, they demand to know more but can't find the end of the string much less pull strings. MJ12 is not in the phone book, does not have a budget, is run by people who have parallel titles within the bureaucracies, so as an organization MJ12 is invisible.
Those who are in the know are people whom MJ12 has contacted. They choose, and introductions or inquiries simply don't come from the other direction. Those in the know are contacted because MJ12 desires something from them - services or cooperation or knowledge. These most often are individuals who already have security clearance, be they former military or current government employees or private citizens sworn in. By being enlightened these individuals pay a price, as joining the greater MJ12 organization is like joining the Mafia - one does not quit. The rules are strict. No profiting by your knowledge, no refusing to abide by the MJ12 board rulings, and no talking. The penalty can be, and has on occasion been, death. Consequently, this group is relatively small, numbering a few hundred, and is only increased in size by new members when there are extenuating circumstances.
Quite frankly, elected officials rarely fit the bill. Not talking is antithetical to politicians, who earn their living by hot air. Politicians tend to be deal makers with soft principles, and the power that comes with the knowledge that membership in MJ12 provides can be heady. Politicians would get themselves killed, on a regular basis, and as they are public figures this would prove awkward. They are left in the dark as this is the lesser of two evils and for their own good.