Results from the last election were remarkable for Democrats among whites under 45 and I don't think that fact has gotten enough attention. This is a big chunk of the white population and if it is truly slipping away from the Republicans that blows quite a a hole in the GOP's white voters-oriented strategy.
Using the Catalist data, which I believe is by far the most accurate data currently available, I find that Democrats carried the national House vote among whites under 45. Ditto for the Iowa gubernatorial election, the Minnesota Senate and gubernatorial elections, the Arizona Senate election, the Virginia Senate election, the Montana Senate election, the North Dakota Senate election and the New Hampshire gubernatorial election. Wow. That's every statewide contest Catalist has released so far, with the exception of the Georgia gubernatorial election, where whites under 45 were nevertheless significantly less Republican than older whites. I think I detect a pattern!
Whites under 45 in the electorate include the leading edge of the the Post-Millennial/Gen Z generation, the entire Millennial generation and the younger, more liberal half of Gen X. The logic of generational replacement suggests that the behavior we now see among whites under 45 will spread farther up the age distribution (i.e., into the higher turnout late forties and fifties) as the years tick by.
If I was a Republican, I'd be pretty damn nervous.