Who serves as the Secretary of Defense according to the text?

The Honorable James Mattis serves as the Secretary of Defense, a position to which he was appointed and confirmed during the Trump administration. As Secretary of Defense, Mattis was responsible for overseeing the Department of Defense, formulating military policies, and advising the President on defense matters. His extensive background as a four-star general in the United States Marine Corps and his leadership roles in various military campaigns provided him with the expertise needed to effectively manage the nation's defense operations.

In contrast, the other figures mentioned held different roles or positions. Mike Pence served as Vice President, Donald Trump was the President, and Richard Spencer held the position of Secretary of the Navy, which is separate from the Secretary of Defense role. Understanding the hierarchy and specific responsibilities of each position is important in recognizing the significance of the Secretary of Defense within the overall structure of the U.S. government and military.