In an Oval Office meeting, Mr. Trump told startled aides that if Attorney General Jeff Sessions would not order the department to go after Hillary Clinton and James B. Comey, the former F.B.I. director, Mr. Trump would prosecute them himself.
Recognizing the extraordinary dangers of a president seeking not just to weaponize the criminal justice system for political ends but trying as well to assume personal control over who should be investigated and charged, the White House counsel, Donald F. McGahn II, sought to stall.
"How about I do this?" Mr. McGahn told Mr. Trump, according to an account verified by witnesses. "I'm going to write you a memo explaining to you what the law is and how it works, and I'll give that memo to you and you can decide what you want to do."