it is showtime for kids. The wall is climbed over, tunneled under, walked around. They come by boat. There are many miles where no wall can be erected. They come through Canada. They walk through the desert. Trump is selling an imaginary defense to people who are too lazy or stupid to figure things out. The ones they catch go to guards and ask for asylum. That gives them some legal rights until their court case. Real illegals can evade the wall.
There were fewer immigrants when Trump was in office because of his horrible mishandling of Covid. Far fewer people were traveling during Covid. They were terrified of catching it.
This is just a reductio ad absurdum fallacy. Walls and barriers do work. They may not stop everyone, but they can and do reduce the number that successfully enter illegally.
Aside from that there are additional measures that can be taken:
Make it illegal to obtain any sort of government identification from a driver's license to whatever. You are here illegally, you can't get these forms of ID.
Make it illegal for anyone who isn't in the country legally and can't prove it, to enter into a contract of any sort. You can't buy a car, can't rent an apartment. You can't buy a home or land.
Make it illegal for anyone without legal identification and proof they are legally in the country to wire money anywhere out of the country.
Make it illegal for anyone who is here illegally to open or hold a bank account.
Of course, make it illegal for persons illegally here to obtain employment.
Make it legal that any law enforcement agency can arrest anyone here illegally and mandatory that they report such arrests to CBP and ICE.
Make "sanctuary cities etc.," illegal.
Enforce the laws against employers who hire illegals.
If that were done, you can bet 90% of the illegals here would flee the country because they don't want to risk arrest, see no value in staying, and are scared shitless that they'll be fucked if caught.