The US Constitution does NOT apply to Mexican Invaders.

Preamble to the US Constitution:

"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our POSTERITY, do ordain and establish this Constitution for the United States of America."

Posterity:

1 : the offspring of one progenitor to the furthest generation
2 : all future generations

Plain and simple, the US Constitution does not apply to them.