Former Vice President Joe Biden's record on racial justice is being re-examined as he hops in the 2020 race for the Democratic presidential nomination.

Biden's mid-1970s crusade against busing as part of efforts to integrate America's schools has resurfaced.

In a 1975 NPR interview, Biden contended busing was a "rejection of the whole movement of black pride."

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In the mid-1970s, a young Democratic senator from Delaware and self-declared liberal who would one day serve as the vice president to the first black president in US history emerged as one of the most vocal opponents of a main force in the integration in America's schools.

Former Vice President Joe Biden, 76, was once at the forefront of a movement against busing students in order to desegregate schools — even battling against Republican Sen. Ed Brooke, the only black senator at the time, over the issue — while he paid lip service to the desegregation movement.

Biden's record on racial justice has become a liability for the former vice president as he joins a crowded, diverse field of candidates vying for the 2020 Democratic nomination. His controversial campaign against busing — the practice of bringing white and black students out of their neighborhoods in order to integrate schools — could haunt him along the campaign trail.

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As he ran for the Senate in 1972, Biden was vocally in favor of integrating America's schools and supported busing.

However, his position on the issue shifted drastically after he won the election when he "discovered just how bitterly his white constituents opposed the method," according to a 2015 Politico article from Jason Sokol, an associate professor of history at the University of New Hampshire who covered the topic extensively in a book on the modern history of race and politics in the Northeast.

By 1973 and 1974, Biden attempted to tow a careful line by vocally supporting desegregation while voting in favor of anti-busing policies. As Sokol described it, Biden's political calculation was "clever but disingenuous."

"History has not been kind to the defenders of school busing. Indeed, busing was problematic — as it transported children long distances away from nearby schools," Sokol added. "But to say most whites objected to busing because it was inconvenient would be wrong. The truth is that many of them were not comfortable with the racial change that busing brought."

Busing was an inherently racially-charged issue, and Biden seemingly wanted to appear loyal to his liberal convictions while he simultaneously worked to appease his uproarious white constituents.

"Biden's opposition to busing was largely a response to the sentiments of his white constituents. You can certainly say that he capitulated to his anti-busing constituents," Sokol told INSIDER in February. "But it's up to you whether you want to characterize those as 'racist sentiments.'"

As opposition to busing became more extreme among his constituents, Biden "morphed into a leading anti-busing crusader — all the while continuing to insist that he supported the goal of school desegregation, he only opposed busing as the means to achieve that end," Sokol said. Biden played a vital role in pushing other liberals to oppose busing as well, according to Sokol.

In 1975 — the same year Biden sided with conservatives by sponsoring an anti-busing amendment — the future vice president attempted to defend his anti-busing stance in an interview with NPR. At the time, Biden described busing as a "rejection of the whole movement of black pride."

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"I think the concept of busing ... that we are going to integrate people so that they all have the same access and they learn to grow up with one another and all the rest is a rejection of the whole movement of black pride, is a rejection of the entire black awareness concept where black is beautiful, black culture should be studied, and the cultural awareness of the importance of their own identity, their own individuality. And I think that's a healthy, solid proposal," Biden, who was 32 at the time, said.

In his 2007 autobiography, "Promises to Keep," Biden described the mid-70s debate over busing as a "liberal train wreck." Biden said that due to his position on the issue at the time some of his colleagues pulled him aside and asked "how and when 'the racists had gotten to me.'"

Biden did not immediately respond to a request for comment from INSIDER.

Then-Sen. Joe Biden on September 19, 1994. Chris Martin/Getty Images

Like many politicians who've spent years in Washington, Biden has a mixed record many issues, but particularly on race relations and criminal justice.

Biden drafted the infamous 1994 crime bill, signed into law by former President Bill Clinton, that many have cited as one of the driving factors behind mass incarceration and the disproportionate imprisonment of people of color.

At a public appearance earlier this month, Biden said he's not "always been right" on criminal justice, but said he's "always tried." As Biden alluded to mistakes that were made back in his Senate days, some seemed to interpret this as an apology for the impact of policies he pushed for while in Congress.

Read more: Biden played key role in pushing US to take hardline stances on crime in 1990s, and now he's apologizing as 2020 looms

Biden for the most part, however, has typically refused to apologize for the 1994 crime bill, and in a 2016 interview contended it "restored American cities."

During his time as a senator, Biden led the charge for Democrats in their war on crime and drugs.

In a 2015 interview with Time, Biden said, "I am not only the guy who did the crime bill and the drug czar, but I'm also the guy who spent years when I was chairman of the Judiciary Committee and chairman of [the Senate Foreign Relations Committee] trying to change drug policy relative to cocaine, for example, crack and powder."

Biden, throughout his career, has also strongly supported affirmative action, worked to expand voting rights, addressed workplace discrimination, introduced the Violence Against Women Act to help victims of domestic violence, and fought to expand the definition of hate crimes. During his time in the Obama administration, he worked alongside former President Barack Obama in championing criminal justice reform.

Sokol said Biden's role in crafting the 1994 crime bill will be more likely to hurt him with voters than his opposition to busing in the 1970s.

Sokol told INSIDER he's not sure how much this issue could "haunt Biden" as he runs in 2020, but added "it could certainly hurt him in the Democratic primaries, where African-American voters (as well as white liberals) wield considerable influence."

"I think Biden's stance on busing is likely to hurt him less than the 1994 crime bill – and perhaps less than his actions during the Anita Hill hearings," Sokol added. "That's because most white Americans regard busing as a failure; even white liberals remain divided about the wisdom of busing."

"Was a busing a success? In some places, yes. In others, not so much," Sokol added. "A lot of it depends on which city you're dealing with."