This will be shot down in court simply because the US does not have a Safe Third Country Agreement with Mexico. The US only has such a law with Canada. Without that agreement with Mexico, US law does not recognize Mexico as a safe third country and, therefore, migrants cannot be rejected for asylum in the US on the basis that they should've applied for asylum in Mexico instead. That's simply not permissible under existing American asylum laws.
Link to source
It should be shot down, but there will be a lot of suffering in the meantime, and I don't have faith in the Supreme Court to uphold the actual law, and it will work its way there.
I know, it must be so hard that the U.S now had the same asylum law as every other country on Earth. I know you wanted the border to remain a breeding ground for human trafficking and the migrants a stump from which Democrats could offer fake tears, but you'll have to make do
If only we had the same healthcare, education, and human rights standards as those same countries. But of course we only opt to adopt the
harmful laws of other countries, not the legitimately helpful ones.