The funny thing that Trump and his supporters don't seem to understand just how unlikely it is the wall will be completed.
Let's say the Democrats do something stupid and cave in to budgetary demands for the wall right away. Well, that's just the early budget for it. Work on the wall won't start for a while. It will likely take years to complete, and that's assuming it doesn't need additional funding rounds or run into major setbacks (both of which are likely).
The problem, of course, is that Trump or another pro-wall Republican President is not guaranteed to be in office during the construction. Work on the wall stops the millisecond a Democratic President takes office. And with increasing chances that Trump is out after the 2020 election, there could be hardly any work done before the wall is canceled. Even if you ignore the many moral objections to the wall, the truth is that it's likely to just be a waste of money that will never be finished in any significant way.