No legal basis. Doesn't have to be one when President Bush calls these people vigilantes, and incites Mexico against them. Shows us what kind of man took over the Republican party.
So many Americans are dumb as clods. The Mexicans hold up signs that say, "Hey, gringo we owned this country before you did, and we have come to take it back." (Outright treason.)
Now who do you suppose taught the Mexicans this lie? Answer: the two Mexican presidents - George Bush and Vicente Fox.
You never hear the Pubs trying to set the historical record straight by reminding people that we fought, bought and paid for the Southwest and Mexico as usual took the money and ran. Less than 40 years of Mexican occupation, (in reality neglect).