Thirty-one percent chose Bernie Sanders, followed by 18 percent for Barack Obama and 11 percent for Mrs. Clinton. Mr. Trump scored highest among Republicans, at 9 percent. In USA Today, Mr. Luntz called it a “a chasm of disconnection that renders every prominent national Republican irrelevant with the voting bloc that could control campaigns for the next 30 years.”

■ Among Republicans, Mr. Trump has retained popularity with the young. He recently led the G.O.P. field at 26 percent among those 18 to 34. But 26 percent was lower than Mr. Trump’s support among G.O.P. backers over all.

■ In looking at all the available exit polling from Republican contests, only in New Hampshire was there a consistent pattern of rising support for Mr. Trump as voting groups got younger. The more typical result was North Carolina’s: 30 percent support for Mr. Trump among those 17 to 29; 37 percent among those 30 to 44; 44 percent among those 45 to 64; and 41 percent among those 65 and older.

Maybe the young are more immune to Mr. Trump’s appeals to ethnic, religious and racial resentment, as an Upshot reader, Stacy from Manhattan, recently suggested:

One of the cheering things about teaching, as I do, an occasional college course is looking out at my 21-year-olds and seeing the total ease at which black, Hispanic, Asian and white students of all ethnicities interact with one another. Over several years, I’ve never had a single incident of disrespect. And the white students are in the main from the exact demographics Trump exploits: middle and lower-middle class, who are less educated and less secure. Many of my students are the first in their families to go to college. As one white young man of Italian ancestry said recently, “All that crap about people’s race or sexuality or whatever — no one our age cares about any of that.” And all the other students nodded and murmured in agreement, including the black and Hispanic ones. I cling to this, because otherwise, the whole country seems to me to be direly sick, a real mess.

Recent research on race is far more pessimistic. Several articles last year poked holes in notions that younger whites were “post-racial,” or significantly less racist than their parents. Writing for Politico, Sean McElwee said millennials “are racially apathetic” and “simply ignore structural racism rather than try to fix it.”