The US is always thought to be protected somewhat by its geographical position with the Pacific Ocean on one side and the Atlantic Ocean on the other.
However as time goes by and technology improves than threats from the south may increase, present trend is set to sign in order to begin process of creating the next generation of missile-defense. The order will call for creation of an iron dome for the US
Trump also wants to distance the US from being the protector of all and of course focus on America, and it’s borders. This is congruent with the idea