President Trump can easily deport millions people without expending any significant effort, dollars, or manpower and do it humanely without splitting up families or penalizing the hardworking illegal migrants already here.
My idea came from the way legal papers are normally served. You can hire a process server who will track someone down and physically serve them with the papers. But in cases where the parties are co-operative, they can sign an acceptance of service and avoid the cost and hassle of actual physical service. By accepting service, while they are not actually physically served, they are legally served.
Deportation could be handled similarly. Those here illegally could be given the opportunity to come forward and sign an "Acceptance of Deportation" and remain in the USA. I would call it "Deportation in Place" and it would be a legal deportation, but not a physical deportation. They could simultaneously apply for legal entry "back" into the country even though they have never actually physically left. There could be a guarantee that they would not be physically deported during the time their application is in process, and that process could be handled at a leisurely pace with minimal additional staffing, there would be millions to process and it could take years without any political fallout.
If the immigrants that come forward are found to be criminals or unacceptable for legal admission, actual physical deportation could then occur. Most importantly, those that don't come forward and accept the deportation in place could be subject to actual physical deportation should they be found to be here illegally, perhaps incidentally to traffic violation or any other minor run in with authorities. Work permits could be offered while the legal entry request was in process, green cards issued to those approved that could include an eventual path to citizenship. Fines could be levied through payroll deduction, taxes would be paid and the millions of illegals could be brought out of the shadows without rounding them up and physically deporting them splitting up families and causing incalculable human suffering. Fines or taxes paid could be channeled to fund the completion of the wall to minimize further illegal entry.
A legal fiction to be sure, but a very workable one that honors President Trump's campaign promise to deport those here illegally.
Another possible bonus would be if the registry of those coming forward for "deportation in place" could be cross referenced to Voter roles and Census data so that those here illegally are prevented from participation in activities reserved for citizens and those here legally.