(Reuters) - U.S. Democratic presidential contender Beto O’Rourke told a conference of black activists on Wednesday that he would back a study of reparations for descendants of slaves, as 2020 White House candidates began to make their pitch for African-American support.

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Two other Democratic contenders, Andrew Yang and Julian Castro, also told the conference organized by prominent civil rights activist Reverend Al Sharpton that they would sign a bill in Congress to create a commission to study reparations.

The three Democrats, the first of a dozen 2020 presidential candidates who will speak to the conference over the next three days, also backed criminal justice reforms including the legalization of marijuana and clearing the records of non-violent drug offenders.

Other Democratic contenders have embraced a bill sponsored by U.S. Representative Sheila Jackson Lee to create a reparations commission, although O’Rourke had not taken a stance until Sharpton asked him about it.

O’Rourke, a former Texas congressman, pledged his support with a reference to the civil rights advances of recent decades.

“Until all Americans understand that civil rights are not just those victories but the injustices that have been visited and continue to be visited on people, we will never get the change we need to live up to the promise of this country,” he said.

Reparations has become a prominent issue in the Democratic race for the nomination to challenge Republican President Donald Trump, and Sharpton praised Castro for helping to bring it to the forefront.

“Our country will never truly heal until we address the original sin of slavery,” Castro, a former San Antonio mayor and U.S. housing secretary, told the conference.

The historically diverse 2020 Democratic field, including black, Hispanic and openly gay candidates as well as a record six women, is tackling an array of issues of interest in the African-American community following the first decline in their turnout in 20 years in 2016. That was a key contributor to Democrat Hillary Clinton’s stunning loss to Trump.

After a question from Sharpton, O’Rourke said police violence was the byproduct of a “larger system - not just of criminal justice in this country. But a system that has successfully suppressed some Americans based on their race for as long as we have been a country.”

The conference in New York is giving activists from around the country a chance to judge the candidates in person. The sessions will continue on Thursday and Friday.

Sharpton said not everyone would agree with the candidates on everything, but support for voting rights, healthcare access and criminal justice reform were “not negotiable for us in the civil rights movement.”

Democrats are grappling with ways to address Trump’s sometimes polarizing racial comments and what polls have found are rising racial tensions since Trump became president.

The candidate who can win African-American support stands to reap significant rewards, as black voters play a big role in Democratic primaries. In South Carolina, which holds an early primary in February 2020, more than 60 percent of the Democratic primary voters were black in 2016.

Sharpton has met with several candidates, but plans to hold off on an endorsement until later in the year.

Who is running in 2020: tmsnrt.rs/2TPLavP