Joe Biden met Thursday with a group of Southern black mayors representing millions of voters in urban centers who could play a key role in the 2020 Democratic presidential primary.

A day after the latest presidential debate in Atlanta, Biden was joined by the city’s mayor, Keisha Lance Bottoms, who has already endorsed him as the party’s nominee. She made her case to mayors from cities including Birmingham, Alabama; Little Rock, Arkansas; Jackson, Mississippi; and Richmond, Virginia, as to why they should also consider backing the former vice president.

“This is about winning,” Bottoms told the group. “I give the analogy that if we agreed on everything, we’d be engaged. This is about a marriage.”

The meeting is a signal of the importance of black voters to Biden’s bid for the Democratic nomination. He’s faced a series of controversies and gaffes as a candidate but remains in the top tier because of his significant support from black voters. His other primary rivals have struggled to court black voters or erode Biden’s support with the most loyal and consistent constituency in the Democratic Party.

“I think Joe Biden’s lock on the black vote is because of the trust they have in him,” said Richmond Mayor Levar Stoney, who has not endorsed a candidate in the primary. “They saw that President Obama trusted him, and they see no reason why they shouldn’t trust him, either.”

In September, the mayors of Columbia, South Carolina; New Orleans; Jackson; and Birmingham wrote an open letter offering a roadmap for presidential campaigns seeking their endorsements, calling for details on how they would address issues including affordable housing, economic development, support for small business, criminal justice, climate change and infrastructure.

Jackson Mayor Chokwe Lumumba said he’s looking for a candidate who can prioritize the concerns of black voters in Mississippi, one of the poorest states. The state has a black population that votes 98% Democratic.

“Southern black cities have always played a role in close Democratic primaries,” said Lumumba, who has reached out to the primary candidates with his agenda. “As I shared with the vice president, when people asked me, ‘How did we feel after Trump became president?’ I told him: I woke up in Mississippi. … We’ve been experiencing being at the bottom for a long time.”

Birmingham Mayor Randall Woodfin said he appreciated the conversation with Biden, which focused on issues including housing, criminal justice and health care.

“He spoke from the heart and attached it to policy,” Woodfin said, pointing out that mayors of the four largest cities from Georgia, Mississippi, Alabama and Arkansas were in attendance. “How those cities perform is usually how the state goes in a Democratic primary. That can’t be ignored.”