By Maggie Haberman and Jonathan Martin, New York Times

CHARLESTON, S.C. — As he left Martha Lou’s Kitchen, a soul food institution here, on Wednesday, Edward Gadsden expressed irritation about the Republican determination to block President Barack Obama from selecting Justice Antonin Scalia’s replacement on the Supreme Court.

“They’ve been fighting that man since he’s been there,” Gadsden, who is African-American, said of Obama, before pointing at his forearm to explain what he said was driving the Republican opposition: “The color of his skin, that’s all, the color of his skin.”

When Sen. Mitch McConnell of Kentucky, the majority leader, said after Scalia’s death on Saturday that the next president, rather than Obama, should select a successor, the senator’s words struck a familiar and painful chord with many black voters.

After years of watching political opponents question the president’s birthplace and his faith, and hearing a member of Congress shout “You lie!” at him from the House floor, some African-Americans saw the move by Senate Republicans as another attempt to deny the legitimacy of the first country’s black president. And they call it increasingly infuriating after Obama has spent seven years in the White House and won two resounding election victories.

“Our president, the president of the United States, has been disrespected from day one,” Carol Richardson, 61, said Wednesday as she colored a customer’s hair at Ultra Beauty Salon in Hollywood, South Carolina, a mostly black town near Charleston. “The words that have been said, the things the Republicans have done they’d have never have done to another president. Let’s talk like it is, it’s because of his skin color.”

Reflecting on the Supreme Court vacancy, Bakari Sellers, a former state representative from Denmark, South Carolina, likened the Senate treatment of the president to the 18th-century constitutional compromise that counted black men as equivalent to three-fifths of a person.

“I guess many of them are using this in the strictest construction that Barack Obama’s serving three-fifths of a term or he’s three-fifths of a human being, so he doesn’t get to make this choice,” Sellers said. “It’s infuriating.”

The anger and outrage that McConnell’s position has touched off among African-Americans could have implications for the presidential election. Leading African-American Democrats are trying to use it to motivate rank-and-file blacks in the party to vote in November, the first presidential election in a decade in which Obama will not be on the ballot and in which Democrats fear black participation could drop.

“Anger becomes action when it’s directly tied to a moment, and the moment now is the election on Nov. 8,” said Stacey Abrams, a Democratic state representative from Georgia and the House minority leader there, adding that Scalia’s death meant that this presidential campaign could no longer be construed as a mere “thought exercise.”

For Hillary Clinton, who is increasingly relying on nonwhite voters to ensure her success against Sen. Bernie Sanders of Vermont, the court issue could be especially crucial. Should Clinton defeat Sanders, who has electrified many liberals, she will need a motivating issue to bring Obama’s loyalists to the polls. She moved swiftly Tuesday to tap into the anger of blacks over the opposition of Senate Republicans to Obama’s naming a replacement for Scalia.

“Now the Republicans say they’ll reject anyone President Obama nominates no matter how qualified,” Clinton said in remarks before a predominantly black audience in Harlem. “Some are even saying he doesn’t have the right to nominate anyone! As if somehow he’s not the real president.”

Doing so, Clinton added, is in keeping with a long-standing pattern of mistreatment.

“They demonize President Obama and encourage the ugliest impulses of the paranoid fringe,” she said. “This kind of hatred and bigotry has no place in our politics or our country.”

Republicans are especially sensitive about the notion that they are diminishing Obama because of his race, and spokesmen for several Republican senators, including McConnell and Sen. Tim Scott of South Carolina, declined to comment.

The suggestion that racism is playing a role angers McConnell’s friends, who point out that his formative political experience was working for a Republican senator who supported civil rights, that he helped override President Ronald Reagan’s veto of sanctions against the apartheid government in South Africa and that he is married to an Asian-American woman.

But in the aftermath of McConnell’s statement on Saturday, a growing chorus of black voices is complaining that such a refusal to even consider a Supreme Court nominee would never occur with a white president.

“It’s more than a political motive — it has a smell of racism,” said Rep. G.K. Butterfield, D-N.C., the chairman of the Congressional Black Caucus.

“I can tick instance after instance over the last seven years where Republicans have purposely tried to diminish the president’s authority,” Butterfield said. “This is just really extreme, and leads me to the conclusion that if this was any other president who was not African-American, it would not have been handled this way.”

Even as Obama’s popularity has risen and fallen, his base of support among black voters has been unshakable. A Gallup tracking poll showed this month showed that some 85 percent of African-Americans approved of the president’s performance compared with only 36 percent of whites. And many African-Americans strongly identify personally with Obama, and have watched his tenure with pride.

Butterfield said that he believed that the effort to undermine, and even delegitimize, Obama began soon after he was sworn in, and that congressional Republicans had blocked Obama’s agenda wherever they could. Even more stinging were the suggestions from some on the right that Obama, a Christian, is actually a Muslim and that he was not born in the United States.

In interviews, members of the Congressional Black Caucus also bitterly recounted indignities, such as demands — most pointedly from the current Republican front-runner in the polls, Donald J. Trump, in 2011 — that Obama prove he was born in Hawaii, and not in Kenya, as some critics claimed. Others recalled the calls to impeach Obama over his use of executive authority.

“You hear the thing about: ‘He’s not a citizen. He oversteps his bounds. He’s divisive.’ One thing after another,” said Rep. Marcia L. Fudge, D-Ohio. “This has been going on since the day he was elected in 2008.”

Republicans have had more success than Democrats in recent decades galvanizing their voters over who should control the courts. But Jennifer McClellan, a member of the Virginia House of Delegates and the Democratic National Committee, said the dispute over how to replace Scalia could now become “an issue for the average citizen.”

Abrams agreed, saying the Supreme Court and its powerful influence on people’s lives is especially resonant with blacks. “Congress is denying our president his rights as a president, but, more than that, they’re denying the legacy of his presidency,” she said. “That will animate Democratic voters across the board but especially African-Americans, who realize more than many voters how great an impact the Supreme Court can have on freedom.”