Sanders has endured a series of crushing defeats in states with large black electorates. Despite heavy spending on TV and paid canvassers in South Carolina, Clinton beat him by more than 70 points among African American voters there and in Georgia— and by a whopping 85 points in Alabama. On Saturday, she won the Louisiana primary 71 percent to 23 percent, again thanks to her strong showing among black voters.

Without stating it explicitly, the Sanders campaign has made no secret of a strategy targeting whiter states. His advisers have argued repeatedly that he retained a path to the nomination that involved winning industrial — and whiter — Midwestern states. Campaign adviser Tad Devine talked about the need for the campaign to “pick our targets.”

Knowing that South Carolina wasn’t likely to tilt his way, Sanders left the state for 48 hours ahead of the primary to campaign in more heavily white states later on the calendar. He targeted five states in the run-up to Super Tuesday, all of them with relatively small black populations. He won four of them. Ahead of Saturday’s contests, Sanders did very little campaigning in Louisiana. Instead, the campaign celebrated a trio of caucus conquests over the weekend in overwhelmingly white states: Kansas, Nebraska and Maine.

Richard Dickerson, a political consultant based in Birmingham, Ala., who has worked on campaigns across the country, said Sanders’s inability to gain traction with black voters leaves him little choice but to focus on states that are less diverse.

“I think that’s the best they can do,” Dickerson said. “It highlights their inability to reach the Democratic base.”

Winning the black vote was always going to be a challenge for Sanders. He is up against the Clintons and their decades-long political relationships with African American leaders and voters. And as a longtime independent, he has never been active with the Democratic party. Elected to the U.S. Senate from Vermont — a state that is 95 percent white — he has none of the relationships that the Clintons enjoy among Democratic activists.

“I think the easy part of getting black voters to turn to Bernie Sanders is what happens when they actually listen to him,” said Ben Jealous, a Sanders supporter and former leader of the NAACP. “The hard part is getting beyond the Clinton brand. The Clinton brand is a bit like Coca-Cola. You know, it’s a Southern brand. Everybody knows it. It tastes good. The question you have to ask is: Is it the best option for you?”

Additionally, Sanders has connected with very few black leaders and voters — although it’s not clear whether he missed opportunities or those individuals were unreceptive to him. The Sanders campaign disputes, for instance, the premise of the question posed to him Sunday in Flint by Bryn Mickle, the editor of The Flint Journal.

Mickle noted that Sanders had visited the city “just over a week ago.” In fact, Sanders first made Flint a campaign issue in mid-January, when he called for Gov. Rick Snyder’s resignation, saying the Republican “knew about the lead in Flint’s water” and “did nothing.” Sanders’s statement came on the eve of a weekend visit to South Carolina and appeared aimed at least in part to get the attention of that state’s African American voters.

The campaign also disputes the perspective of Flint Mayor Karen Weaver, who said with some bafflement that Sanders didn’t make an effort to contact her. “It’s very interesting to me that he hasn’t called,” said Weaver, who endorsed Clinton in mid-January and wore a large gold pin with the campaign’s logo on her lapel at the debate in Flint on Sunday. “It seemed to me that he’d talk to the mayor of any city he visits that is in crisis and asked what we in government need.”

Briggs, from the Sanders campaign, said the mayor was mistaken. “We tried to meet with her,” he said. “We called. We went to City Hall and waited outside her office. We invited her to the opening of a Flint field office. She never responded. She also did not show up at the very moving town meeting at the church in Flint.”

The Sanders campaign is by no means targeting white voters exclusively. One campaign ad, featuring the daughter of Eric Garner, who died when New York City police officers used a chokehold to restrain him, is clearly meant to convey his support for the Black Lives Matter movement.

In addition, he has collected endorsements from a group of famous African American supporters, including academic Cornel West, film director Spike Lee, actor Danny Glover, entertainer Harry Belafonte and rapper Killer Mike, who all have vouched for how his agenda would benefit African Americans. Killer Mike has gone so far to say has Sanders would help carry on the legacy of Martin Luther King Jr.

While Clinton enjoys far broader back among black elected officials, several have stepped forward to support Sanders, including Rep. Keith Ellison (D-Minn.), who was among Sanders’s biggest cheerleaders in his state, and former Ohio state senator Nina Turner, who has a national profile among Democratic activists. In South Carolina, a half-dozen African American lawmakers who also campaigned on Sanders’s behalf.

But there are signs that he hasn’t reached out to black voters in the traditional manner of Democratic politicians. Sanders has demonstrated that he can draw large crowds almost anywhere in the country — including thousands to a rally in Ann Arbor on Monday. But he has not fully embraced another staple of the campaign trail: retail politicking.

Clinton peppers her schedule with visits to restaurants, workplaces and houses of worship, providing opportunities to talk to voters in small groups or one-on-one (with TV cameras capturing the moment, of course).

Sanders has seemed a fish out of water during his relatively few attempts to mingle with everyday people. On a Sunday morning, he’s much more likely to appear on a network talk show than in a pew of an African American church. That aloofness may have hurt him, particularly among African Americans in the South. Rather than coming into their communities, Sanders was only seen as a northerner talking at them in large settings.

Supporter Killer Mike seemed to understand that. He told reporters he wanted to take the senator on a barber-shop tour throughout the South. Sanders visited a barbershop in Atlanta owned by Killer Mike — who widely distributed a video of their discussion there — but a tour never happened.

Sanders also stumbled in Sunday’s debate, when he answered a question about whether he has any “racial blind spots” by suggesting that only black people live in ghettos.

“When you’re white, you don’t know what it’s like to be living in a ghetto. You don’t know what it’s like to be poor. You don’t know what it’s like to be hassled when you walk down the street or you get dragged out of a car,” Sanders said.

Jealous, who was at the debate, acknowledged that Sanders’s answer missed the mark, but he criticized Clinton for failing to mention in her answer that as a high school student she supported Republican Barry Goldwater, who ran for president in 1964 on a platform opposing the Civil Rights Act. In her autobiography, Clinton writes about her transformation from Republican to liberal Democrat.

Ellison noted that there are parts of Bill Clinton’s legacy that should give black voters pause, including welfare reform, a crime bill that has been blamed for ushering in the era of “mass incarceration” and NAFTA, which has hurt African American workers in industrial states.

That argument does not appear likely to affect the outcome in Michigan, which votes Tuesday. In a new NBC News/Marist poll released Sunday, Clinton leads Sanders 57 percent to 40 percent overall — and 76 percent to 21 percent among black voters.

A commanding Clinton victory in Michigan Tuesday would render Sanders’s path to the nomination all but impassable. And that, in turn, raises the question of whether it’s even possible to win the Democratic nomination without the black vote.

The answer is no, said Dickerson, because many of the states that yield the largest number of delegates have significant percentages of black voters in the Democratic primary electorate. “It’s all about the delegate count.”