The Rev. Jesse Jackson Sr. on Sunday announced his endorsement of Democratic presidential hopeful Bernie Sanders ahead of Tuesday’s pivotal primary in Michigan, a state with a significant African American vote.

Jackson’s public support for Sen. Sanders, a Vermont independent, came shortly after Democratic frontrunner Joe Biden picked up the endorsement of Sen. Kamala Harris, D-Calif., a former presidential candidate who is black.

Jackson, a Chicago civil rights icon and two-time former presidential candidate, backed Sanders a day after the socialist firebrand drew thousands of supporters to a rally at Grant Park in advance of the March 17 Illinois primary.

Later Sunday, Jackson appeared at a Sanders rally in Grand Rapids, Michigan. The state is now a crucial battleground for Sanders, who has fallen behind the former vice president in the delegate count.

“With the exception of Native Americans, African Americans are the people who are most behind socially and economically in the United States, and our needs are not moderate,” Jackson said in a statement issued by the Sanders campaign.

“A people far behind cannot catch up choosing the most moderate path. The most progressive social and economic path gives us the best chance to catch up, and Senator Bernie Sanders represents the most progressive path. That’s why I choose to endorse him today.”

Jackson is no stranger to presidential politics.

The leader of the Rainbow/Push Coalition staged a pair of unsuccessful presidential bids in 1984 and 1988. Jackson’s issues then resembled Sanders’ platform, including plans to provide free community college for all and create a single-payer health care system. Sanders, who was mayor of Burlington, Vermont, in 1988, endorsed Jackson for president then.

In the 1988 Democratic primary, Jackson earned 6.9 million votes and won 11 primary contests. Michael Dukakis, the former Massachusentts governor, ultimately won the party’s nomination but lost to George H.W. Bush in the general election.

Sanders’ key competitor in the Democratic primary also made a short-lived run for the party’s nomination during that election cycle. On Sunday, Jackson said Biden’s campaign didn’t seek his endorsement in the current race.

Biden is ahead in the delegate count after scoring a series of victories on Super Tuesday and South Carolina. Sanders took aim at Biden’s voting record during Saturday’s rally, slamming his opponent’s support for the Iraq war, the Wall Street bailout, the abortion-related Hyde Amendment and trade agreements, like NAFTA.

This weekend’s endorsements by Jackson and Harris come at a critical time, as the African American vote is a factor in this week’s Michigan primary.

Perhaps the Harris endorsement healed a rift.

On Friday, at a fundraiser in north suburban Glencoe, Jill Biden was asked about the potential of Harris being a vice presidential pick if her husband is the nominee. Jill Biden said remarks the California senator made at a debate last summer hit Biden like a gut punch.

At that debate, Harris confronted Biden on his remarks she said were defending his working with two segregationist senators. Harris called those remarks “hurtful.” Biden said at that debate he never defended “racists.”

Jill Biden said Harris had a very close “bond” with the Bidens’ son, the late Beau Biden, who was a Delaware attorney general. When Joe Biden looked surprised on the debate stage, Jill Biden told the Glencoe group it was because “our son, Beau, spoke so highly of her and you know, and how great she was. And not that she isn’t, I’m not saying that. But it was just like a punch to the gut; it was a little unexpected.”

In addition to Michigan, Biden and Sanders will face off Tuesday in five other primary elections.