Julián Castro on Sunday blasted Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE as “a coward” for raising questions about the racial heritage of Sen. Kamala Harris Kamala HarrisHundreds of lawyers from nation's oldest African American sorority join effort to fight voter suppression Biden picks up endorsement from progressive climate group 350 Action 3 reasons why Biden is misreading the politics of court packing MORE (Calif.), a fellow 2020 Democratic presidential hopeful.

The president's eldest son last Thursday retweeted and then deleted a post by Ali Alexander, a conservative media personality, claiming that Harris “comes from Jamaican Slave Owners” but is “not an American Black.”

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“Is this true? Wow,” Trump Jr. tweeted to his 3.65 million followers before deleting it.

Castro on Sunday called the move “disgusting” and said it “has no place in our politics.”

"You notice what he did. He tweeted it out, and then he deleted it like a coward so he could say, 'Oh, that was just a mistake,' but he knows what he’s doing. He’s giving voice to these racist, you know, utterances about Sen. Harris," he said on CNN's "State of the Union."

"We need to dispel them immediately and condemn them and then not give them any more life because they’re disgusting," he said.

Harris delivered one of the biggest moments of last Thursday’s Democratic presidential debate by challenging former Vice President Joe Biden Joe BidenPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Hillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Fox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio MORE about his past opposition to federally mandated busing to integrate public schools.

She said busing personally affected her life and criticized Biden for touting his collegial relationships with segregationist senators James Eastland (D-Miss.) and Herman Talmadge (D-Ga.), calling those words “hurtful.”

“I do not believe you are a racist and I agree with you when you commit yourself to the importance of finding common ground," she told Biden at the debate.

"But I also believe, and it’s personal and I was actually very — it was hurtful to hear you talk about the reputations of two United States senators who built their reputations and career on the segregation of race in this country," she added.