“Kyrsten Sinema, you couldn’t tell the difference between her and Martha McSally on matters of the border,” he said. “She did not run as a Democrat, she ran as an independent or an Arizonan, and did not concede one bit of being tough on illegal immigration to Martha McSally.”

Demographers have long predicted the growing share of Latinos in Texas and Arizona would turn those Republican-leaning states a shade of purple or blue. Democrats’ expectations of awakening “the sleeping giant” of Latino voters have been repeatedly thwarted.

But 2018 may have moved them a step closer to the future. More than one in four Latino voters said they cast a ballot in a midterm election for the first time, versus 12 percent for whites, according to the Pew Research Center. In congressional races across the country, about 69 percent voted for the Democrat.

“Immigration is the big deal breaker in not voting Republican,” said Joseph Garcia, director of the Latino Public Policy Center at Arizona State University.

Because Latinos are much younger on average than whites, and many are just forming a partisan preference, Mr. Garcia predicted that Mr. Trump’s policies and language about immigrants would sour them on Republicans in federal elections for years to come.

“It wasn’t just the wall, it was the rhetoric over three years demonizing Latinos in general,” he said. “That has a longer-lasting effect than just this administration.”

“The die has been cast in that Arizona’s future is largely Latino,” he added, “and they’re all U.S. citizens because they were born here.” The median age of Latinos in Arizona is 26, and for non-Hispanic whites, 43.