Nonwhites are growing as a share of the electorate faster in the West than they are elsewhere. For the first time, minorities in 2012 accounted for at least 30 percent of the eligible voting population in Arizona, Nevada and Alaska — all states where Republicans currently hold top statewide offices. Colorado, where Mrs. Clinton’s campaign is so confident of a victory now that it has has no plans to buy advertising time through Election Day, is also approaching 30 percent.

The demographics were already daunting. But many Republicans now say Mr. Trump is only accelerating the flight of minority voters to the Democratic Party, like dry underbrush feeds an Arizona wildfire…

Most demographers did not believe Arizona could be truly competitive for Democrats in a presidential election until 2020 at the earliest. But Mr. Trump’s unpopularity has spawned a demographic double threat that has implications in Arizona and beyond: He is not just weak among Hispanics, but also with with educated white professionals who have moved to places like Denver, Salt Lake City and Phoenix in search of better jobs and a lower cost of living…

“Arizona is on the cusp,” said Ruy Teixeira, a senior fellow with the Center for American Progress, who studies the political implications of population shifts. “And if it is on the cusp this fast, I think that means these other states become even farther out of reach.”