Also, there's a reason for the pressure on Paul Manafort.
Why was he in the Russia meeting? He wasn't there because Jr told him to go. He was there most likely because Trump Sr wanted the leader of his campaign in the room to get the dirt on HRC from Putin.
A candidate conspiring with a hostile foreign power, a FOE, against US democracy isn't presidential material.
Naturally, Trump's obstruction exists because he is concealing the truth.