As it says in the title, your challenge is to make the US have an Exective Office or Presidency composed of 3 more or less equal parts.
Could the role be divided and what would they be - eg Commander-in-Chief, Supreme Judge, Head of Senate?
What about in stead of having an election after the primaries, have the two final candidates of the two majority parties as Two of the Executives, with the one holding the majority being known as "Federal President" and the second being "Federal Chancellor".
For example in:
~ 1912, Wilson and Roosevelt.
~ 1960, Kennedy and Nixon sit as president.
- The two running mates are created duel vice-presidents, with the one holding majority being given the Head of Senate and the other being Head of Representatives
- Have an election to elect Commander-in-Chief, usually from high ranking military.
This puts the five remaining people to be known as Councillors in the Federal Council.
This is 7 executives, same as Switzerland. If you want more, how about:
Addition to these 7, what if the council also had to hold the Governors from each state. This puts 59 executives around the council

hope this meets the AHC
