And i wonder why isn't it just used for it's purpose: quickly find and deport any undocumented migrant. If their origin country can't be established or refuses to accept them, just lock them up in gulags and populate some public database with photos, fingerprints etc. - until someone picks them up to take away e.g. relatives. Put their fingerprints into database for life, repeat offence just means gulag until too old to reoffend again.

Prison population too high? Fix this "supply side", build much much bigger, much cheaper gulags than today's fancy, small prisons - U.S. has a warm climate, that won't be hard or expensive or too torturous - and make sure criminals and delinquents know that these will fit EVERYONE. Make them work (say build roads) to pay for that.

And yes, U.S. needs a 24/7 physically defended border. Russia has it being a much poorer much sparser populated country with a much longer border, so U.S. can too. No "refugess", "asylum seekers" etc. You try to cross border without papers or outside of designated crossing points - you get a bullet.