I think the fruit of the poisonous tree doctrine WOULD apply if the case were being heard in a court. What is going on here, though, is that Mueller strategically chose to not make a finding that would have led to criminal charges. Instead, he wrote a report that will be used by the Democrats to impeach in the House and that is not a judicial proceeding, it's a legislative proceeding. I'm not an expert on these things, but I believe Congress creates its own rules for an impeachment proceeding, and only if they choose to include the fruit of the poisonous tree doctrine would it apply. And you can bet that the Democrats will NOT include this in the House proceedings.
