Even if everyone in Washington has the best of intentions, a Wall is unlikely to be built anytime soon, given the the logistical, legal, and bureaucratic challenges. And Democrats don’t have good intentions. If they take back Congress, surely one of their first priorities will be to defund and stop whatever Wall has been authorized.
Also, border security, properly considered, is about much more than the Wall — it requires all sorts of resources and authorities to make sure that people who are caught at the border don’t make it into the country anyway. Are Democrats going to accede to those?