You don't have to actively send them all back. You just remove welfare benefits. You make sure no jobs are taken by anyone here illegally. You make employers responsible to use the e-verify system and penalize them if they hire without doing so. You stop sanctuary cities. You disallow sending money out of the country by anyone who cannot prove they are here illegally. You deport those who commit crimes when caught. You enforce existing laws. Etc.
80% will self-deport. The 20% can be handled. The wall will keep them from swarming in continually.
Sounds great to me. But this isn’t what Trump said, (wish he would have because it is far more realistic and detailed than “they’re going back and the good ones can come back in”).