It was leaked to Mccain, reporters, which then allowed the FBI to quote those sources to use the fake steele dossier has the truth.
In short, no matter how many convictions mueller get's it's all the result of manufactured false evidence.
Which, due to the fruit of the poisonous tree legal doctrine, will give them all a chance to have the convictions appealed, and tossed out.
https://www.law.cornell.edu/wex/fruit_of_the_poisonous_tree