WASHINGTON — Gregory Cheadle, the man whom Donald J. Trump famously called “my African-American” at a California campaign rally, watched this month as now-President Trump praised the “very fine people on both sides” of the deadly melee in Charlottesville, Va., and he decided that possessive word “my” was in grave danger.

His backing for the president is on “life support,” he said.

Shermichael Singleton’s support has flatlined. Mr. Singleton was fired from his job as a senior adviser for the Department of Housing and Urban Development in February after previous writings critical of Mr. Trump came to light, yet he remained supportive. No more.

As the president headed to Phoenix on Tuesday to preach national unity at a campaign-style rally, even ardent supporters in the African-American community said the ties that once connected them to Mr. Trump had frayed badly.

“It’s difficult to continue to have hope for President Trump,” Mr. Singleton said. “It’s difficult to focus on complex policy issues when you have a country that is falling apart. It’s difficult to focus on health care. It’s difficult to focus on the economy. It’s difficult to focus on infrastructure when you have people who dislike other people because of their ethnicity.”