Highly likely they knew, and used this as a lever to get what they wanted.
It may be being used, now, to insure he keeps the "correct" narrative going.
Hmmm... Not convinced. Not sure how his past convictions would be any leverage. The current charges could be. But he’s been charged anyway.
Maybe they thought this would be an embarrassment to Trump to be associated with Nader. But in my view its humiliating to Mueller that they would rely on him at all - and that they cited his name 100+ times in the report released in April when they knew at least 6 weeks earlier he would be charged for child porn.