The Framers of the US Constitution, in 1787, felt that it was important that the President, in his (originally, or her), role as Commander-in-Chief, have no other allegiances. It was then, and is now, a wise requirement.
It never seemed to bother them much before a brother made it into the White House. Jackson would not have qualified under some of the 'opinions' offered on the topic, nor would have Chester A. Arthur. But since it's never been adjudicated by the Supremes, there is no authoritative ruling to point to.
And I'm not even sure about George Washington, John Adams ,Thomas Jefferson, James Madison, James Monroe and John Quincy Adams - none of whom were born in the United States.