Gov. Andrew M. Cuomo continues to hold a dominant lead over Cynthia Nixon, according to a new Siena College poll of likely Democratic primary voters, outpacing the activist and actress by 31 percentage points with less than 50 days until the primary.

Mr. Cuomo tops Ms. Nixon across every part of the ideological spectrum, every region, every racial group, every age, and among both men and women. His strongest support remains in the African-American community, with the 75 percent of black voters supporting the incumbent governor, compared with only 19 percent for Ms. Nixon.

Both candidates have aggressively courted black voters, a community seen as critical to Democratic primaries in New York. On Sunday, Ms. Nixon endorsed Jumaane Williams, an African-American city councilman from Brooklyn running for lieutenant governor, as her insurgent running mate, and they campaigned together again on Monday.

Mr. Williams is challenging Mr. Cuomo’s No. 2, Lt. Gov. Kathy Hochul, and the Siena College poll showed that as a far more competitive race. Ms. Hochul leads Mr. Williams 30 percent to 21 percent, with half of voters still undecided.