History Tidbits: 20th President of US needed a metal detector

Who was the 20th President of the USA?  Hints:

He was the last of the “log cabin” presidents.

His assassin shot him in the back and arm.  He died in 1881 after serving only 200 days as 20th.

His inept doctor was possibly responsible for his death, as history says he could have survived his wounds.

His death helped launch the crude invention of the metal detector by Alexander Graham Bell.

Robert Todd Lincoln, first son of Abraham Lincoln, serving as this president’s Secretary of War was with 20th at the moment the assassin’s bullets struck.

So, who was the 20th?  James A. Garfield