Can a president stay in office past the end of his or her term in the event of a war?
Article II of the U.S. Constitution defines a presidential term as four years, and literally not a minute more. The 20th Amendment specifies the transition time and date as noon on Jan. 20. Federal law detailing presidential war powers does not discuss term extensions in the case of war. No emergency-powers statutes appear to allude to the possibility.
There is no precedent for an extension of a term. Previous states of war have not disrupted the four-year election cycle. The election of 1864 was held during the Civil War, reelecting President Lincoln in a landslide. In 1940, after World War II had broken out but before the U.S. had entered it, President Roosevelt won a third term, and in 1944, as the Allies were advancing towards Germany, a fourth. (The 22nd Amendment, limiting presidents to two terms, was ratified in 1951.)
