I read on https://ktla.com/news/california/san-ysidro-border-line-waits-grow-to-10-hours-in-coronavirus-crackdown/ (mirror):
The crackdown comes after U.S. Customs and Border Protection said it surveyed about 100,000 travelers coming from Mexico by car or on foot and found 63% of U.S. citizens and legal residents traveled for reasons that were not essential.
But I don't see any sanction being imposed, so I'm not sure what they mean by crackdown here, and checking for the reason of stay in Mexico after leaving Mexico seems a bit late for pandemic purpose.
Do the US or Mexican authorities impose any sanction if a US lawful permanent resident (LPR) (and who is a French citizen) comes back from Mexico to the US via land border after having traveled from the US to Mexico via land border for non-essential reasons?