In a remarkable interview with CNN's Jake Tapper today, the president's lawyer Rudy Giuliani suggested it was possible — and would be "perfectly normal" — that Trump talked to Michael Cohen before he testified about him to Congress. Giuliani added he didn't know if Trump and Cohen had such a conversation.
Why it matters: It's not "perfectly normal" for subjects of or witnesses in a Congressional investigation to discuss testimony directly with each other. If witnesses or subjects are talking to each other, the government can always claim one is trying to influence the others' testimony. That's why lawyers counsel against doing it.