Set aside what you think of guns or immigration as a matter of public policy or even morality.
Instead, think of them as dye-markers of how our cultural politics and the nature of the two political parties have changed over time.
In the 1990s, it was common for Democrats to fret over both illegal and legal immigration. "All Americans," President Clinton said in his 1995 State of the Union Address, "are rightly disturbed by the large numbers of illegal aliens entering our country."
Meanwhile countless Republicans championed immigration.
"I'm hard pressed to think of a single problem that would be solved by shutting off the supply of eager new Americans," then House Majority Leader Dick Arney said in 1994. "If anything, we should be thinking about increasing loyal immigration."
House Speaker Newt Gringrich said, "I think we would be a very, very self-destructive country if we sent negative signals on legal immigration."
As for firearms: Democrats passed an assault weapons ban in September 1994. However, Clinton indicated that that decision was one of the chief reasons the GOP took back the House two months later.
True or not, the more important consequences was that gun rights became more and more a partisan issue, and the NRA had little choice but to become an adjunct of the GOP.
Guns and immigration are not simply drivers of polarization; they are examples of its power. Politics has become a lifestyle, part of the "big sort" driving so much in our culture.
Liberals like Sen. Bernie Sanders have talked about "two Americas" for generations, but they worked on the assumption that the divide was class-based.
It is not. It's cultural, and the divide is becoming a chasm.