NEW YORK — Democratic presidential candidate Hillary Clinton delivered a barbed and unmistakable message to rival Sen. Bernie Sanders on Tuesday: Do not expect to show up at the last minute and claim African American voting support to which she a has long and powerful claim.

Speaking in Harlem, surrounded by New York elected officials and African American leaders, Clinton suggested that Sanders is a Johnny-come-lately to racial justice issues.

“We Democrats have a special obligation if we’re serious about our commitment” to equality and social betterment, Clinton said. “If we continue to ask black people to vote for us, we cannot minimize the realities of the lives they lead or take their concerns for granted,” she said at the Schomburg Center for Research in Black Culture.

“You can’t just show up at election time and say the right things and think that’s enough,” she said to rousing applause. “You can’t start building relationships a few weeks before a vote and think that’s enough.”

That was a reference to Sanders's recent inroads in South Carolina, the first broad test of black voting strength in the 2016 contest. Clinton's hastily-announced address is part of a push to engage black voters and display the depth of her support ahead of the South Carolina primary Feb. 27 and the string of Southern and Midwestern states that vote in March.

She also accused Republicans of allowing or encouraging racist attitudes toward President Obama, and Republican state legislatures of systematically trying to deny black voters their rights.

Republican vows not to confirm any Supreme Court nominee Obama sends to the Senate are a way of discounting his presidency, “as if somehow he’s not the real president,” Clinton said.

“That’s in keeping with what we’ve heard all along, isn’t it?” she said. “Many Republicans talk in coded racial language about takers and losers. They demonize President Obama and encourage the ugliest impulses of the paranoid fringe.”

In an emotional speech frequently interrupted by applause, Clinton proposed new federal-backed school policies to end what she calls overly punitive school discipline rules that disproportionately affect people of color. When a coughing fit pulled her up short, Clinton gratefully took in the wave of applause and chants of "Hill-a-ry" that broke out, masking her coughs.

She spoke extensively about the water crisis in poor, majority-black Flint, Mich., which she asserted would never have happened in a wealthy white town. She wove in references to her long ties to African American leaders and civil rights figures.

“We’ve spent a lot of time debating about the big banks and the excesses of Wall Street,” she said. “But Flint reminds us, my friends, that there’s a lot more going on in our country that we should be concerned about. The truth is we aren’t a single-issue country.”

Her $2 billion plan would encourage the hiring of "School Climate Support Teams" in districts and schools with high suspension and in-school arrest rates. She said she would invest in and reward school districts that reform their school discipline programs.

"If they do the right thing, we’ll have their backs," she said. And for those that don't, she said she would recommend that the Justice Department intervene.

"This is a civil rights issue and we cannot ignore it," she said.

Clinton's campaign cited opinions of principals, administrators and teachers that some public school discipline policies make it more likely that African American students end up on a path toward prison.

Clinton's campaign cited federal statistics to show that zero-tolerance discipline policies are part of the reason that black boys are three times more likely to be suspended and black girls are six times more likely to be suspended than their white peers.

The disparity begins as early as preschool, according to the campaign.

While black students represent 16 percent of student enrollment in American public schools, they represent 27 percent of students referred to law enforcement and 31 percent of students subject to a school-related arrest, according to Clinton's campaign.

Earlier Tuesday, Clinton met with the Rev. Al Sharpton and a small group of other civil rights leaders at the National Urban League's headquarters on Wall Street. Sanders met with many of the same leaders last week.

"The only disagreement we had is when she didn’t support me for president, but I got over that,” Sharpton said, drawing a chuckle from her and the other eight civil rights leaders in the room.

He did not announce an endorsement.

“I look forward to talking about the agenda that each of you have put forth, giving you my ideas about what we can do to be effective and making clear that I’m not a single-issue candidate,” Clinton said.

That was a dig at Sanders and his focus on issues of income inequality.

Participants included Marc H. Morial, president of the National Urban League; Melanie Campbell, head of the National Coalition on Black Civic Participation; and NAACP President Cornell W. Brooks.

Hillary Clinton on the campaign trail

CLEVELAND, OH - On the third day of a bus tour through Pennsylvania and Ohio, Democratic Nominee for President of the United States former Secretary of State Hillary Clinton along with running mate Senator Tim Kaine, and Anne Holton, aboard the campaign bus in Cleveland, Ohio on Sunday July 31, 2016. (Melina Mara/The Washington Post)