It could happen much faster than you think. If the border is secured, then step up strict enforcement of all immigration laws. At this point those being deported are not simply coming back so the deportation numbers are actually reducing the population here. When the illegals realize they can no longer work, access services, and if they are arrested they will be deported a large number will simply begin to go back on their own. It is not a fantasy and there would be no need to actually deport each one, for everyone deported many would just leave. They poured in here because we put out the welcome mat, if we pull up the mat they will pour out.
Basically what I said only you’re trying to say a lifelong liberal we should put no trust in is going to do it.