You might want to get a copy of Stephen Hunter's book about the 1950 assassination attempt on President Truman, "American Gunfight: The Plot to Kill President Truman--and the Shoot-out That Stopped It"

The guns used by the Secret Service presidential protection detail have changed a lot over time. I don't know how you'd find out.

I'd expect that places like White House TN, OH, TX, etc. are likely too small to have more than a constable.