War! What is it good for?
Trump showing his ignorance of history again. The Secretary of War was traditionally the name for the senior civilian executive of the U.S. Army, like Edwin Stanton under Lincoln. There was also a secretary of the Navy, like Gideon Welles. After World War II, a really nasty interservice fight broke out between the Army and the Navy over which service secretary would be supreme in the post-war Pentagon, and as a compromise, the Secretary of Defense (as well as a Secretary of the Air Force) was created under the National Security Act of 1947.
So if Trump changes Hegseth's title to Secretary of War, he could be opening a huge can of DoD political worms for himself, since SECNAV and SECAF won't like it one bit. And SECARMY won't like being bigfooted by a renamed SECWAR.