“...there is a very good legal basis to exclude Mexicans under category #2...”
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If the law is passed, can it be applied retroactively? That would really be a step in the right direction.
Politically, the only way to make it fly might be to (1)affirm birthright citizenship for those who had it before the law went into effect and (2)to allow children born of foreign parents who were in the country legally to apply for the same right under the 14th amendment as was granted automatically to children of parents who were not in the country legally.
The threat of retroactive revocation of wrongly acquired birthright citizenship could be enough to get the powerful ethnic lobby to agree to no more going forward to get a grandfather clause for those already here.