In a black-and-white photo released by the Chicago Tribune from its archives Saturday morning, two police officers can be seen grabbing hold of a young man wearing glasses. His mouth agape, he crouches forward and resists their grip. To his right, an older man in black watches stoically with a cigarette in his right hand.

The captive young man, as it turns out, is 21-year-old Bernie Sanders, today a senator from Vermont and a presidential hopeful. At the time of the photo in 1963, Sanders was a student at the University of Chicago, an avid civil rights activist and a leader of the Congress of Racial Equality. In this particular moment of strife, he was being taken by Chicago police toward a police wagon following a protest against school segregation in the Englewood neighborhood of the city.

1963 arrest photo of young activist Bernie Sanders emerges from Chicago Tribune archives https://t.co/0zYArWlYwx pic.twitter.com/bnWonq0nwn — Chicago Tribune (@chicagotribune) February 20, 2016

"Bernie identified it himself," Tad Devine, a senior adviser to the Sanders campaign, told the Tribune. "He looked at it – he actually has his student ID from the University of Chicago in his wallet – and he said, 'Yes, that indeed is [me].'"

"His activism and when it occurred, as a young college student, set in motion the direction of his life," Mr. Devine added.

As his support among African American voters has thus proven to be tenuous next to his opponent Hillary Clinton, this photograph will perhaps reinforce Sanders’s identity as an activist and ally of civil rights causes, especially at a time when America’s black electorate is galvanized by what can be considered a new civil rights movement.

In the Nevada caucuses Saturday, Ms. Clinton’s victory was bolstered by an overwhelming majority of black voters – 76 percent, according to entrance polls. Although the numbers were much closer in Iowa and New Hampshire, where Sanders won, experts anticipate that Clinton will maintain her edge among African Americans in the upcoming primaries.

According to a Bloomberg poll published last week, the former secretary of state leads Sanders by 22 points overall and nearly 40 points among likely black voters. The Clintons have successfully established an alliance with black preachers and politicians in South Carolina, at least in part thanks to the efforts of former President Bill Clinton. What happens next Saturday will likely determine how each candidate will fare in other racially diverse states.

“It’s a really interesting race, and Clinton’s ability to do well among African-American voters is one of the biggest stories so far, in part built on the fact that she’s been building relationships in the African-American community for a very long time,” Gibbs Knotts, a political scientist at the College of Charleston, told The Christian Science Monitor’s Patrik Jonsson Saturday.

Both Clinton and Sanders have aggressively courted the loyalty of black voters since the start of their campaigns, and both have attained at least moderate success.

Both candidates have focused on issues like mass incarceration and police brutality. They’ve also had their share of hiccups – rally interruptions from Black Lives Matter for Sanders and in one particularly offensive gaffe, Clinton said the phrase,” all lives matter.”

But both have found endorsements within the black community. While Clinton has gained the support of Geneva Reed-Veal, the mother of Sandra Bland, Sanders has that of Erica Garner, the daughter of Eric Garner. (The Garner family vote is divided, however. The late Mr. Garner’s mother is a supporter of Clinton). Clinton secured the backing of the Congressional Black Caucus political action committee, and Sanders has an endorsement from Ben Jealous, the former head of the NAACP.

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"Clinton was the person who assumed she would get black voters, and Bernie Sanders knew he needed to work for them," Eric Guster, a political and legal analyst, told the BBC. "And he came out of the gate working for them."

[Editor's note: The original story misidentified a group that was backing Clinton: It is the Congressional Black Caucus PAC]