Washington (CNN) Donald Trump on Saturday pushed back against Hillary Clinton's efforts to link him to the Ku Klux Klan.

The Republican nominee retweeted a supporter's post that the Democratic nominee "said a KKK member was her mentor." And speaking later in Des Moines, Iowa, he dredged up Clinton's use of the term "super predators" in the 1990s to argue that he, not Clinton, offered African-Americans the best choice for president.

Trump's retweet and his latest appeals to black voters capped off a week of increasingly ugly and racially charged accusations between the two leading presidential candidates, during which Trump called Clinton a "bigot" and the Democratic nominee charged that Trump's campaign was built on "prejudice and paranoia" while also tying him to the KKK.

"@DiamondandSilk: Crooked Hillary getting desperate. On TV bashing Trump. @CNN, she forgot how she said a KKK member was her mentor," Trump tweeted Saturday.

"@DiamondandSilk: Crooked Hillary getting desperate. On TV bashing Trump. @CNN, she forgot how she said a KKK member was her mentor. — Donald J. Trump (@realDonaldTrump) August 27, 2016

Lynette Hardaway and Rochelle Richardson -- better known as Diamond and Silk, two African-American sisters supporting Trump who frequently speak at his rallies -- confirmed to CNN that the tweet referred to the late West Virginia Sen. Robert Byrd, a former KKK member whom Clinton mourned in 2010 as "a true American original, my friend and mentor."

"Donald J. Trump can't help who embraces his campaign but Hillary Clinton could've helped who she embraced," the duo said in a statement to CNN.

A Trump spokesman, Jason Miller, declined to comment, and a message left with Clinton's campaign was not returned.

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Trump's surrogates in recent days have pointed to Clinton's relationship with Byrd in response to accusations that Trump's campaign stokes racial tensions.

Thursday night, Trump supporter Scottie Nell Hughes also cited Byrd, telling CNN's Anderson Cooper, "(Clinton) sat there and praised Sen. Byrd saying that he was her mentor, that he should be respected and he was a leader of the KKK."

And on Friday, Trump supporter Kayleigh McEnany, speaking to CNN's Jim Sciutto on "The Lead," said Trump's campaign was not engaging in Clinton's "gutter politics."

"You have heard no language to this level coming out of the Trump campaign," McEnany said. "They could be digging into her past with Robert Byrd."

Accusations of bigotry

On Wednesday, Trump flatly labeled Clinton a "bigot who sees people of color only as votes, not as human beings worthy of a better future."

The Democrat soon after told Cooper that Trump "courted white supremacists" and "is someone who is very much peddling bigotry and prejudice and paranoia." The next day, she gave a speech in Nevada accusing Trump of "taking hate groups mainstream and helping a radical fringe take over the Republican Party."

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Her running mate, Virginia Sen. Tim Kaine, picked up on that line of attack Friday, saying Trump was "pushing" the values of the KKK. He backed away from the comments on Saturday, telling reporters in Florida that Trump has some supporters "connected" with the KKK who are "claiming him."

Trump has described such attacks as attempts to "smear" his supporters. And recently, he's tried to reach out to African-American voters, describing black communities as filled with high crime and high unemployment and asking, "What the hell do you have to lose?"

Trump sought again on Saturday to draw African-American voters -- a reliably Democratic demographic -- to his campaign, noting that "Republicans are the party of Abraham Lincoln" and arguing that minorities would benefit from his presidency.

"Nothing means more to me than working to make our party the home of the African-American vote once again," Trump said while speaking before a nearly all-white audience at Iowa Sen. Joni Ernst's "Roast and Ride" event.

At the same event, he referenced Clinton's use of the term "super predators" in 1996 to describe violent criminals, a term widely seen as racist and that Clinton has said she regretted using.

"By the way, how quickly people have forgotten that Hillary Clinton called black youth 'super predators.' Remember that? 'Super predators.' And they were very, very insulted, but now people have forgotten," Trump said.

Meanwhile, Clinton, in a statement Saturday commemorating the 53rd anniversary of the March on Washington, said "the stakes in this election are unlike any we have faced before."

"Those brave men and women who marched, and sat, and bled for civil rights in American must not have done so in vain," Clinton said, though she did not mention Trump's name.

Byrd and the KKK

Before entering national politics, Byrd helped organize a 150-member chapter of the Klan in Sophia, West Virginia, in the early 1940s . He was chosen as the group's leader.

Byrd wrote in his autobiography that he "reflected the fears and prejudices" of those years and that he mainly joined the Klan because he identified with the hate group's anti-Communist politics.

As a senator, Byrd spent more than 14 hours filibustering the 1964 Civil Rights Act, a decision he later regretted.

"I saw the act in the kaleidoscope of life, liberty and property," he told CNN's Dana Bash in 2006. "That was a different time. I'm from the South, grew up in a Southern home ... and it was that Southern atmosphere in which I grew up and with all of its prejudices and its feelings."

Byrd told Bash he considered his involvement with the KKK "the greatest mistake of my life." He said he hoped young people learned from the mistakes of his youth.

He even went so far as to apologize to then-Sen. Barack Obama in 2005 for his Klan membership.