"According to Leon Panetta, the Obama administration did not place much trust in Mattis because he was perceived as too eager for a military confrontation with Iran.[70] Panetta later said Mattis lacked "the maturity to look at all of the options that a president should look at in order to make the right decisions"."
https://en.wikipedia.org/wiki/Jim_Mattis#:~:text=According%20to%20Leon%20Panetta%2C%20the,to%20make%20the%20right%20decisions%22.