If Donald Trump does not wish to collaborate in the destruction of his presidency, he will refuse to be questioned by the FBI, or by a grand jury, or by Special Counsel Robert Mueller and his malevolent minions.
Should Mueller subpoena him, as he has threatened to do, Trump should ignore the subpoena, and frame it for viewing in Trump Tower. If Mueller goes to the Supreme Court and wins an order for Trump to comply and testify to a grand jury, Trump should defy the court.
http://buchanan.org/blog/memo-to-trump-defy-mueller-129254