Some states have increasingly opted for 'internal' controls, involving the exclusion of undocumented migrants from government services and the arrest of undocumented migrants away from the border.
He also said he would deport millions of undocumented migrants.
Many melted into the already large population of undocumented migrants in the border area.
The simple aim of recent immigration and border policy: Reduce the inflow of undocumented migrants.
And every year tens of thousands of undocumented migrants are sent home.
If that happens, America's population of undocumented migrants might decide it is safest, after all, to remain in the shadows.
Along with introducing draconian measures to curb the influx of undocumented migrants, he wants to slash legal immigration.
Meanwhile, he seems to be placating Washington by stepping up arrests of undocumented migrants heading through Mexico.
When a heckler in November pleaded that he had the power to halt deportations of undocumented migrants, he replied: "Actually, I don't".
The National Human Rights Commission of Mexico says thousands of undocumented migrants are kidnapped and held for ransom by drug gangs in Mexico each year.
Forcing every Muslim in the country to register for some sort of database would do nothing to secure the borders or stanch the flow of undocumented migrants.
