Donald Trump's worst enemy is without doubt his own mouth, and it has his lawyers sweating...umm...bullets.
Yesterday I heard several legal experts who were asked if Donald Trump has to speak to Robert Mueller's investigators under oath. Their unanimous answer: yes he does. Some Supreme Court decision awhile back (Nixon...Clinton?) said if subpoenaed, the President must appear and answer questions. Trump's lawyers can indeed try to negotiate favorable terms for him, but Mueller is in the drivers seat. "I don't remember" will likely backfire as these slick gubment prosecutors can ask seemingly innocent, unrelated questions that are all really leading up to the same answer, one they already know the answer to.
Where Bill Clinton's Rhodes Scholar mind carefully considered the question before he answered "it depends on what the meaning of 'is' is", Trump will just blurt out whatever first comes into his mind. He doesn't understand the concept of "the powerful pause" before answering. Proof? See yesterday's "shithole African countries" comment.
They said if President Trump's lawyers can't negotiate a deal whereby he can answer written questions with written answers carefully crafted by them, they'll likely advise the President to just pardon everyone remotely involved and then resign.