Of the states where deaths now exceed births for whites, 13 voted for Mr. Trump and 13 voted for Hillary Clinton. Four are states that flipped from President Barack Obama in 2012 to Mr. Trump in 2016 — Ohio, Michigan, Pennsylvania and Florida. It is not clear how demographic change will affect politics in the future.

“People say demographics is destiny and there’ll be more people of color — all that is true,” said Jennifer Richeson, a social psychologist at Yale University. “But they also say the U.S. is going to become more progressive, and we don’t know that. We should not assume that white moderates and liberals will maintain current political allegiances, nor should we expect that the so-called nonwhite group is going to work in any kind of coalition.”

At its most basic, the change is about population, but each state experiences it differently.

Florida was the first state where white deaths outstripped births around 1993, largely because it was drawing a lot of retirees. But its population has been one of the fastest growing in the nation. Retirees have kept coming, replenishing the white population, and its large Hispanic population has helped lift the state over all. The median age for Hispanics in the United States is 29, prime for child bearing, compared with 43 for whites.

Deaths began to exceed births for whites countrywide in 2016, according to the report. But in many states, as in Florida, white people moving in made up the losses. However, in 17 states, including California, Michigan, New Jersey and Ohio, those migrants weren’t enough and the white populations declined between 2015 and 2016, said Kenneth M. Johnson, a demographer at the University of New Hampshire and the report’s other author. Five of those states registered drops in their total populations that year: Vermont, West Virginia, Pennsylvania, Mississippi and Connecticut.