[lawtguy]

The 13% you mentioned I'm assuming is the percentage of the US population that is foreign born. That is not the highest in US history. Take a look at page 3 of this: https://www.census.gov/newsroom/pdf/cspan_fb_slides.pdf (sorry for the PDF). You'll see that 13-14% foreign born was pretty much the norm from 1860-1920. The US society seemed to survive that just fine.

To your point though, I suspect a lot of older voters grew up with much lower immigration (due to the Immigration Act of 1924) and so this level feels really high to them even though it was common for a large part of US history.