Second Nephi 1:7

Wherefore, this land is consecrated unto him whom he shall bring. And if it so be that they shall serve him according to the commandments which he hath given, it shall be a land of liberty unto them; wherefore, they shall never be brought down into captivity; if so, it shall be because of iniquity; for if iniquity shall abound cursed shall be the land for their sakes, but unto the righteous it shall be blessed forever.

Even though the general population may become wicked and bring a curse on America, it will always be a land of promise for the righteous. The righteous may suffer from the curse brought about by wickedness, but they will be spared from the worst.