A source familiar with Ty Cobb's departure says the White House lawyer had been clashing with the President in recent weeks over Trump's combative posture with the Special Counsel's investigation.

"Ty was uncomfortable with the Mueller tweets," the source said. He was not going to be "part of a mud-slinging campaign," the source added.

Cobb had tried for weeks to counsel the President against threatening the Mueller investigation, the source said. Cobb made it clear on multiple occasions with the President and other members of the legal team that he "can't go down that path."