Define "Invasion"...

Originally Posted by Tribesman

But this is a customs and immigration issue so its the primary role of US customs and border protection and US immigration and customs enforcement agencies not the army.
To put it plainly its a police matter.

Customs is for people entering through legal checkpoints and channels.

Immigration determines who may enter, through legal checkpoints and channels, and may deny entry to some, or force the deportation of others.

When the numbers entering through non-legitimate channels reaches into the millions, it's an invasion. The purpose of an army, is to defend their country's border.