Though Mr. Trump’s campaign announced a new Asian Pacific American Advisory Committee last week, a Republican National Committee spokesman, Ninio Fetalvo, said Mr. Trump’s outreach to Asian-American voters had been coordinated until now mainly through two staff members at the party’s Washington headquarters. The party, he added, has also printed materials in a variety of Asian languages in cities like Las Vegas.

Republicans’ difficulties with Asian-Americans are similar to those the party has faced with most minority groups. A sense that the party is hostile to immigrants and minorities has driven more Asian-American voters into the Democratic Party lately, political scientists and community leaders said. And if Republicans do not make more of an effort, those voting shifts could harden, just as Hispanics’ voting patterns have.

“What we see now are some early indications that people who either leaned toward the Democratic Party or did not identify with either party are now starting to identify as Democrats,” said Karthick Ramakrishnan, a professor of political science at the University of California, Riverside. “This is still a group that is making up its mind,” he added, “but it should be concerning to the Republican Party that you’re starting to see this crystallization.”

A national survey in the spring by Asian and Pacific Islander American Vote, a nonpartisan research group, showed “a significant leftward shift” since 2012 among Asian-American registered voters, with 47 percent now identifying with the Democratic Party, compared with 35 percent in 2012. Fifteen percent identified as Republican.

In 1992, the year national exit polls started reporting Asian-American sentiment, the group leaned Republican, supporting George Bush over Bill Clinton 55 percent to 31 percent. But by 2012, that had reversed. Asian-Americans overwhelmingly supported President Obama over Mitt Romney — 73 percent to 26 percent, almost the same margin by which Hispanics favored Mr. Obama.

A Pew Research Center report released last month showed that Asian-Americans have since 2008 embraced the Democratic Party at a faster rate than any other ethnic group.