Border Enforcement:
Put trained up snipers at the border and very publicly spend a week or two firing on all alien trespassers. It will stop in short order. A dozen body bags is about what it would take to fully stop decades of this insanity.
Repatriation of Illegals:
Again, a few no-nonsense raids of enclaves of illegals, at workplaces or hangouts, or on known multi-family households, a dozen or so heads kicked in, maybe a few killed trying to resist, and millions would start running for the border or lining up voluntarily to leave.
Will Rubio change parties? It is too easy to imagine the tear-filled “My heart told me I just couldn’t stay with those immigrant-hating Republicans” speech, that never mentions all the legal immigrants who played by the rules.