You have no idea about how effective a large contingent of well-armed, pissed-off Americans will be (the majority of whom will likely be hunters and expert marksmen) at stopping these turds from crossing onto our soil.
Since you have aptly stated the unwillingness of our leaders to do anything effective, and since this emergency is happening now and thus “electing new leaders” is not a practical solution to the PRESENT NATIONAL EMERGENCY, that automatically puts the ball in our court. If our leaders lack the resolve to stop these invaders, then it is our moral duty to stand in the breech.
I have a very good idea of how effect such forces would be. The answer is not very effective.
It won't be from any lack of skills or determination.
The enemies have organized propaganda and firepower (Mexican Army, Police, and Cartel forces) to back their demands. They also have a substantial "fifth column" of Leftist supporters in this Country. We have indecisive political leaders at the State, County, and Municipal levels who will actually move to stop volunteer forces from doing anything effective.
That has to change before volunteers can be a decisive force. The Police and Military forces will need directions from their commanders to avoid confrontations with American volunteers. The political Authorities (or their replacements) will need to give those directions.
On the plus side, the Mexican forces will probably turn on each other at the first setback and destroy themselves. This invasion will disintegrate at the first real opposition.
We have not seen that yet. Let's not get too wrapped up in our own propaganda.
Some appropriate song lyrics to keep in mind about our politicians:
"And if you really want to know our view - you haven't done nothing" (Stevie Wonder)