Biden could solve this problem by making the existing border crossings easier/faster. Last time I was in Mexico it two 3 hours to get back into the US. Border agents could work much faster. Mexicans - like humans everywhere - are mostly nice people. IF congress won't fund more border control then just metrics for how long the line is on the agents "scan the passport, you look like the picture, no red flags in the computer so I need to keep this line moving: NEXT". Just making the legal border crossing easier would make a big difference.