Prosecution of the Great War was the dominating issue for both parties. Outgoing President Woodrow Wilson helped stump for Semmes (his Vice President), insisting that Semmes would lead the country in a sensible, rational way, while Arango was a hot-blooded Mexican who would lead the country recklessly. For his part, Arango did indeed promise more vigorous prosecution of the war, and even proposed putting Confederate Negroes into uniform.
The Red Rebellion broke out a month before Confederates went to the polls, and while this event shocked many whites, it didn't do much to affect either candidate's chances. For most, it simply "proved" how wrong Arango's plan for black soldiers was.
Gabriel Semmes defeated Doroteo Arango on Tuesday, November 2, 1915. Semmes would oversee the end of the Great War and the aftermath of defeat, while Arango went back home to Chihuahua.