More than twice as many Asian-Americans now identify as Democrats than as Republicans, and they hold strongly unfavorable views of Donald J. Trump, a new national survey found, emphasizing the Republican Party’s continued struggle to appeal to minority groups.

The figures, published on Wednesday by the nonpartisan National Asian-American Survey, suggested that the political allegiances of Asians might be hardening in a way that could harm Republicans with the fastest-growing minority group well beyond 2016.

“Over the past 20 years,” the report said, “Asian-American support for Democratic presidential candidates has increased more dramatically than among any other racial group.”

Fifty-seven percent of Asians identify with or lean toward the Democratic Party today, compared with 24 percent who do for the Republican Party, the survey said.