The only way to reverse or slow "the invasion" will be by the use of force.
This force could be "passive", in the form of a border barrier, if we can just get it built.
Failing that, the force used must be "active" -- military troops who will "do what is necessary" to PHYSICALLY prevent the invaders from "crossing the line".
If we're not willing to do one or the other -- or both -- then we have no more claim on the country. It's lost.
Think back to the what the Indians saw happening to their lands, as late as the 1880's. They knew their way of life would soon be lost to the coming of the white man.
At least they TRIED to fight back.
Yet we... are doing nothing.
"The fault, dear Brutus, lies not in our stars... but in ourselves."