Latest "Trump mattis fight" stories
Mattis — who preferred the call sign "Chaos" — has been fighting the "Mad Dog" moniker for at least 15 years.
Sen. Jim Inhofe said that the current Pentagon leader lacks the "humility" of former Defense Secretary Mattis.
The president said he told Mattis to leave the Defense Secretary job because he wasn't successful enough in the post.
The comments come just two days after the popular former Marine Corps general was forced out of his Defense Department leadership post.