They're not going to bother with the amendment because we'll still have 13 red states to say no.
They are not pretending to make any effort to save the republic. In the 19th century Mexico allowed people from the US to settle in Texas. Those settlers overwhelmed the Mexican residents though legal immigration and eventually rebellion. In a way, Our greedy politicians are allowing illegal immigration to reverse that change. But the cartels, not Mexico, are the beneficiaries.