Democratic presidential candidate Bernie Sanders has gone to great lengths to prove he is a politician African-American voters can back. Since launching his campaign in the spring, he has hired an African-American campaign spokeswoman, allowed activists to speak during his well-attended rallies, and uttered the phrase “black lives matter,” a nod to the social justice movement that has spread throughout the nation in recent years. But he has also stumbled by initially saying "all lives matter" and downplaying the effect racism has had on black-white inequality.

An endorsement this week by Cornel West, the prominent civil rights activist and scholar, could be the shot in the arm that Sanders needs to win over black voters who remain skeptical of his credentials on black issues. But contrary to the myth that African-Americans vote together for the same Democratic candidate, the community is likely to continue scrutinizing White House hopefuls in both parties regardless of high-profile endorsements. Support of a prominent figure like West only helps Sanders if he brings to the campaign trail a message that resonates with blacks, political experts said.

“What America needs to understand about black voters is that we’re not a monolithic [block] and that we all don’t listen to or follow under [the] lockstep of Al Sharpton or Jesse Jackson,” said Stacey Hopkins, an African-American who backs Sanders and volunteers for a Women For Bernie support group in Atlanta. Still, Hopkins said it will benefit Sanders that West has credentials among “the generation that arose in the Occupy movement and speaks to the liberation movement that is the platform of Black Lives Matter."

But a figure like West, who has been known to lock arms with activists from the Black Lives Matter movement, also poses risks for Sander’s campaign among black voters. Andra Gillespie, a professor of political science at Emory University in Atlanta, said West angered some in the black community when he very publicly blasted President Barack Obama as out of touch on issues of poverty and criminal justice during the 2012 election cycle. Obama has enjoyed a high approval rating among blacks and garnered more than 90 percent of the black vote in the 2008 and 2012 presidential elections, something that West’s criticisms have not changed.

“Something tells me that Cornel West is going to have to compete in the marketplace of ideas because there are people who are still very skeptical of Bernie Sanders,” Gillespie said. “There’s going to be a very robust debate about which kind of Democratic candidate black voters should get behind.”

West, a prominent voice on social and political issues where race, class and justice intersect since the 1990s, made his announcement Monday night on Twitter. Before his tweet went viral, West explained his decision in a Facebook post:

My endorsement of Brother Bernie in the primaries is not an affirmation of the neo-liberal Democratic Party or a downplaying of the immorality of the ugly Israeli occupation of Palestinians. I do so because he is a long-distance runner with integrity in the struggle for justice for over 50 years. Now is the time for his prophetic voice to be heard across our crisis-ridden country, even as we push him with integrity toward a more comprehensive vision of freedom for all."

Sanders has narrowed his second place standing behind Clinton in recent months. Clinton was leading Sanders by as much 36 points in national polling data in July. The latest CNN/ORC poll had Sanders closing the gap, 47-29 percent among likely primary voters in mid-August.

Sanders, 73, an independent U.S. senator from Vermont, has had to fend off protesters who claim he isn't credible when it comes to reforming the criminal justice system, which disproportionately incarcerates blacks and Latinos and places an emphasis on aggressive policing in communities of color. Black Lives Matter protesters last month disrupted a Sanders campaign rally to demand the candidate speak out against police brutality and white supremacy.

Sanders initially responded by retracing his long history of activism on issues of racial inequality. As early as the 1960s, Sanders campaigned against racial segregation in Chicago public schools. He participated in the Rev. Martin Luther King Jr.-led March on Washington for Jobs and Freedom in 1963. As a member of Congress, Sanders stood against Democrats’ welfare reforms and tough-on-crime policies of the 1990s, which created barriers to public assistance programs that benefited poor blacks and saw millions of black and brown people arrested, jailed and left with criminal records.

But even after he detailed his record to black activists, they continued targeting his campaign rallies. Eddie Glaude Jr., chairman of the Center for African-American Studies at Princeton University in New Jersey, said Sanders is unlikely to get a pass from black voters in the upcoming cycle.

"What Cornel West's endorsement reveals is that African Americans are thinking carefully about the candidates and the importance of this election,” said Glaude, who worked with West when the activist was a black studies professor at Princeton.

"So much is at stake," Glaude added. "We can’t take anything or anyone for granted or be too quick in making summary judgments about where black people stand or who they will vote for.”

Derrick Harkins, senior vice president for innovations in public programming at Union Theological Seminary in New York City, where West teaches, said every black vote will be earned regardless of any high-profile endorsements.

“Cornel West's support for Bernie Sanders is important, and speaks to the development of clearer message of racial justice on Sanders’ part," he said. "However, Bernie Sanders still has work to do to prove that he is the candidate that will best reflect the values of [the Black Lives Matter movement]."

Candace Simpson, a black student at Union and a Black Lives Matter activist, said voters must hold all candidates accountable for institutionalized racism.

"We are talking about political processes and projecting wins or losses when the true matter is much bigger than what happens in 2016," Simpson said. "We recognize the inherent responsibility of political parties and politicians in the oppression of black people. There is no such thing as a politician who is without guilt.”