I would love to know how Trump decided upon the two of them in the first place.
If you aren't familliar with a topic, in his position you'd call in the 'experts'.
Fauci had been the head of the National Institute of Allergy and Infectious Diseases for a while, since 1984, which means he's fairly highly ranked and by virtue of that position, an "expert".
Birx had served under Obama as United States Global AIDS Coordinator for Presidents Barack Obama and Donald Trump since 2014, which made her response coordinator material.
Keep in mind that science isn't supposed to play politics or have an agenda, but provide the right answers, as best we know, without prejudice. Obviously, that isn't what is going on, any more than the Climate Alarmists are neutral.