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.
P.S. I don't blame Mexicans. I love Mexican food by the way.
But we're not handling the flow of migrants in a way that benefits us. And that's intentional like you said. Trump tried but failed. So it's going to get worse. South Africa is a good example of the direction we're heading.