Among the signals that the Democratic presidential race is heating up in the final few weeks before the first round of caucuses and primaries, a leader in Sen. Bernie Sanders’ campaign on Sunday published an op-ed detailing former Vice President Joe Biden’s record on racial issues and encouraging black voters to support Sanders.

In an op-ed for The State—a newspaper based in South Carolina, which will hold the nation’s fourth nominating contest on Feb. 29—Sanders 2020 co-chair Nina Turner, an African American woman, wrote:

Turner highlighted moments from each man’s political career to establish a contrast between them. She pointed to Biden’s votes and advocacy for “bills designed to prevent black students from accessing white schools” compared with Sanders organizing civil rights protests as a college student in Chicago.

Recalling the 1991 hearings to confirm Clarence Thomas as a Supreme Court justice, when Biden chaired the Senate Judiciary Committee, Turner wrote that “Biden facilitated the public degradation of Anita Hill, an esteemed professor already victimized by a powerful man.”

The op-ed also noted Biden and Sanders’ positions on so-called “welfare reform” in the 1990s as well as “tough on crime” legislation and economic policies, including 2005 bankruptcy legislation that Biden backed. “And today, “Turner wrote, “the differences between Biden and Sanders remain stark.”

As Turner explained, Biden “opposes Democratic efforts to legalize marijuana” while Sanders supports not only legalization but also criminal justice reform to address institutional racism; Biden opposes transitioning to a Medicare for All healthcare system, for which Sanders has advocated for years; and Biden “has refused to support Sanders’ bill to make public colleges and universities tuition free and cancel all student debt.”

“By supporting a racial justice champion like Sanders—and his popular progressive agenda—black Americans will forge a multiracial, multigenerational working-class alliance that will generate the high turnout necessary to beat President Donald Trump,” she concluded. “In standing with Sanders over Biden, we will declare that we are not going backward—we are going forward into a future of empowerment and equality for all.”

According to Sanders 2020 speechwriter and senior adviser David Sirota—who wrote about Turner’s op-ed in the most recent edition of BERN NOTICE, a newsletter he authors for the campaign—Turner scheduled multiple televised interviews to discuss her piece for The State.

Ryan Lizza, Politico‘s chief Washington correspondent, tweeted in response to Turner’s op-ed that “this is the whole kitchen sink against Biden.” He added that it “will be interesting to see if Sanders is willing makes these same attacks at Tuesday night’s debate.”