I would think it possible to narrow down to a very small number, or even find out definitively who gave DJT the virus. I would certainly try, in his shoes. The number of people he is in contact with is not infinite. It's not like he ran over to the store to pick up milk for Melania.
one of the tells is you get a little info, but nothing really specific … people will fill in the blanks on their own or wait for more info … that never comes