If you go to the right events people will talk demographics. From a generational perspective America does not have enough taxpayers to keep Social Security solvent. The older generation are retiring in large numbers and there just aren't enough people paying in.
America isn't having enough babies to keep a stable population let alone support all the people moving into social security and medicare.
IMO the politicians are trying to use immigration to prop this up and have been for decades. I know the make up of America has changed significantly since I was a kid.
