Mattis Explains Why He Can't Quit Trump and Yup, It's the Exact Reason You Expect

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President Donald Trump (L) is introduced by Defense Secretary James Mattis (R) during the commissioning ceremony of the aircraft carrier USS Gerald R. Ford at Naval Station Norfolk in Norfolk, Virginia, July 22, 2017. The two men have not always seen eye-to-eye on policy, but Mattis said serving the president was an obligation. Jonathan Ernst/Reuters

Defense Secretary James Mattis has revealed candid information about his relationship with President Donald Trump, with whom he has had some notable disagreements, saying he saw his service as a call of duty, not of choice.

Mattis entered the Pentagon's press bullpen by surprise Thursday, telling reporters that he felt more comfortable speaking to them there than behind the podium. The retired Marine general dismissed claims that he had contradicted Trump on Wednesday by saying diplomatic solutions were possible with nuclear-armed North Korea shortly after the president said talks were out.

Related: Has Mattis gone rogue? The defense secretary has stood against Trump multiple times

Mattis did, however, address some of the other major disputes he's had with the commander-in-chief and why he has not opted to resign, even as the administration continues to be engulfed in controversy.

RTS1CKCM President Donald Trump (L) is introduced by Defense Secretary James Mattis (R) during the commissioning ceremony of the aircraft carrier USS Gerald R. Ford at Naval Station Norfolk in Norfolk, Virginia, July 22, 2017. The two men have not always seen eye-to-eye on policy, but Mattis said serving the president was an obligation. Jonathan Ernst/Reuters

"You know, when a president of the United States asks you to do something - I don't think it's an old-fashioned school - I don't think it's old fashioned or anything, I don't care if it's Republican or Democrat, we all have an obligation to serve. That's all there is to it, you serve," Mattis told Defense News Executive Editor Kevin Baron.

"First time I met with President Trump we disagreed on three things in my first 40 minutes with him, on NATO, on torture and on something else, and he hired me," he added. "This is not a man who is immune to being persuaded if he thinks you've got an argument."

While Mattis did not elaborate on the third point of dispute he had with the president, this was because he did remember, not an intentional omission, Baron reported. As for the other two issues, Mattis has said that he opposed Trump's early views on U.S.-led military alliance NATO as "obsolete" as well as the Republican leader's assurance that "you bet your ass" he would utilize torture techniques, such as waterboarding, against suspects "in a heartbeat."

The comments come days after Mattis lectured U.S. troops stationed in Jordan about problems back home "that we don't have in the military." The pep talk quickly raised speculation as to whether Mattis was indirectly referring to Trump's polarizing public image and even prompted discussions among experts of the possibility of a military coup in the U.S. Some of the perceived spats between Trump and Mattis, however, may appear more serious than they really are.

RTSXPYK President Donald Trump delivers remarks after attending a swearing-in ceremony for Defense Secretary James Mattis (R) at the Pentagon in Washington, January 27, 2017. Trump entered the White House touting a number of non-traditional views of U.S. policy, some of which Mattis has pushed back on. Carlos Barria/Reuters

Mattis appeared to disown Wednesday a tweet posted earlier that day by Trump, who said that "talking is not the answer" to solve the crisis with North Korea after the reclusive, militarized country launched a ballistic missile over Japan on Monday. Mattis later said that there was always a diplomatic solution, but clarified to reporters Thursday that he wasn't referring to talks, but other diplomatic channels.

Mattis also recently ordered a review of Trump's ban on transgender people serving in the U.S. military. Many have portrayed this move as a sign of his opposition to a policy he was reportedly "appalled" by, but it also may likely just be the first signs of Mattis determining how to best implement a policy he himself said "the department will be carrying out under the president's direction."