I would guess that less then 5% would be able to come back
Think about it
If they are on welfare, section 8, food stamps, etc, they are not coming back, they have no valid reason to come here. Fixing illegal immigration fixes many other issues, illegal drugs, crime, rising health care costs, rising public school costs, public assistance costs
That is why what Trump is saying is really important. If he fixes that, he fixes a dozen other problems as well. And he knows that.
You’re absolutely right about turning off the magnet.
If illegals can’t get public assistance and jobs, they can’t survive here. In fact, turning off the magnet is the only thing that will truly stop them from coming here.
No amount of physical barriers or threats is going to deter people who are etermined to escape the hellhole countries they come from.