Hillary Clinton visits a South Carolina Strong nonprofit facility for former felons in North Charleston on Wednesday, Feb. 24, 2016. (Photo by Melina Mara/The Washington Post)

SUMTER, S.C. – Republicans are mounting a “deeply disrespectful” effort to deny President Obama his right to nominate the candidate of his choice for the Supreme Court, Hillary Clinton said Wednesday.

“The president is absolutely right to send a nominee to the United States Senate,” Clinton said angrily. “I find this argument absolutely unbelievable” that Obama should not send up a nominee in this final year of his presidency, Clinton said.

“You have one president at a time.”

It was hardly lost on the overwhelmingly African American audience at a small black college that Clinton was talking about the country’s first black president.

“To say don’t even send us a nominee is at variance to the Constitution and deeply disrespectful to the office of the president of the United States,” Clinton thundered, to roaring applause.

“I’m backing the president. He will send, as he always does, a well-qualified nominee.”

Democratic presidential candidate Hillary Clinton told South Carolina supporters on Feb. 24 that she supports President Obama "100%" in fulfilling his constitutional duty to send a Supreme Court nominee to the Senate. (Reuters)

Clinton is making strong support for Obama a cornerstone of her stump speech in South Carolina this week, as she tries to bolster her already-strong support among black voters.

“What I’m going to do is build on the progress we’ve made under President Obama and go further,” she said Wednesday.

Clinton invoked the names of civil rights icons Rep. John Lewis and the Rev. Martin Luther King Jr. as she railed against what she called efforts to curtail voting rights in some states. Democrats allege that new voting rules in Texas and other states are primarily aimed at limiting the African American vote, although Clinton did not spell that out Wednesday.

“I thought those battles had been fought and won,” she said. “The only way to beat back these kinds of cynical maneuvers is at the ballot box. Vote people out who don’t want you to vote, that’s the best remedy.”

Clinton told an enthusiastic crowd at historically black Morris College that she would expand federal help for historically black institutions under her plan to offer debt-free public education.

The private school, founded in 1908, is among the small private historically black colleges and universities Clinton says would be threatened by her Democratic rival Bernie Sanders’s signature plan for free public college.

Clinton is campaigning heavily across South Carolina ahead of the Democratic primary Saturday, and focusing squarely on African American voters and issues of race, poverty and inequality. She is far ahead of Sanders here and expects to notch a solid victory among African American voters that would establish momentum going into Southern states that vote in March.

Clinton visited a program for ex-prisoners, addressed an all-black union audience and an alumni meeting of the influential African American sorority Alpha Kappa Alpha in the state capital Columbia on Wednesday.

"I do need your help on Saturday," she said at a local office of the Longshoreman’s Association. She helpfully provided the polling hours – 7 a.m. to 7 p.m. “Or you can vote absentee."

Also Wednesday, Clinton debuted a new ad in South Carolina featuring Columbia Mayor Steven Benjamin telling his young daughters that Clinton “will fight for an America where all of our sons and daughters can live up to their God-given potential.”

Benjamin, president of the African American Mayors Association, introduced Clinton with his daughters’ help at the sorority luncheon Wednesday.

A Clinton testimonial ad narrated by actor Morgan Freeman and featuring the candidate talking with African Americans is also playing frequently in South Carolina. Former president Bill Clinton, who is overwhelmingly popular among black voters, is barnstorming the state Thursday and Friday on his wife’s behalf.

Hillary Clinton barely mentioned Sanders during public appearances Wednesday, but her campaign sent out a fund-raising appeal that highlighted Sanders’s votes against immigration reform and in favor of legal immunity for gun manufacturers.

"I think these votes mattered," Clinton says in the email appeal. “Right now, Senator Sanders is running a campaign based largely on a single issue -- but I don’t think we’re a single-issue country,” Clinton’s appeal said, as she asked for donations as small as $1.