Actually it was William McKinley who was President when we took Puerto Rico from Spain in 1898. Teddy Roosevelt was assistant secretary of the US Navy under McKinley (later Vice President when McKinley was re-elected since Vice President Garret Hobart had died in office).
You are correct. Of course Roosevelt and the imperialist wing of the GOP was one of the prime agitators for the war. McKinley was against it and only bowed when it became clear that Congress would declare with or without his approval.