A number of hopefuls for the Democratic nomination for president found common ground Saturday as they defended rival Sen. Kamala Harris against online allegations that she is not an "American Black."

Former Vice President Joe Biden, who clashed with Harris at Thursday's Democratic debate in Miami after she criticized his position five decades ago against school busing, said the social media attacks against the senator from California were clear echoes of "birtherism."

"Birtherism," promoted by some Republicans, including Donald Trump before he assumed the presidency, was a movement that denied former President Barack Obama was a natural-born U.S. citizen, implying he was ineligible to be president.

"The same forces of hatred rooted in 'birtherism' that questioned @BarackObama's American citizenship, and even his racial identity, are now being used against Senator @KamalaHarris," Biden tweeted. "It’s disgusting and we have to call it out when we see it. Racism has no place in America."

Rep. Tim Ryan, D-Ohio, also compared the online attacks, which claim Harris is not a black American because her father is Jamaican, to "birtherism," whose proponents claimed incorrectly that Obama was born in Kenya.

"The attack on @KamalaHarris is racist and we can't allow it to go unchecked," Ryan tweeted. "We have a responsibility to call out this birtherism and the continued spread of misinformation."

Sen. Elizabeth Warren, D-Mass., tweeted, "The attacks against @KamalaHarris are racist and ugly. We all have an obligation to speak out and say so. And it’s within the power and obligation of tech companies to stop these vile lies dead in their tracks."

Other presidential hopefuls who came to Harris' defense included Bernie Sanders, who called Donald Trump Jr. a racist for retweeting a claim that Harris is not a black American; South Bend, Indiana Mayor Pete Buttigieg, who called the attacks racist and "birther-style;" Sen. Cory Booker, D-N.J.; Washington Gov. Jay Inslee, who said, "The Trump family is peddling birtherism again;" Sen. Amy Klobuchar, D-Minn.; Sen. Kirsten Gillibrand, D-N.Y.; and former U.S. Rep. Beto O'Rourke of Texas.

Harris' campaign also compared the allegations to "birtherism."

"This is the same type of racist attacks used to attack Barack Obama," campaign spokeswoman Lily Adams said. "It didn’t work then and it won’t work now."

The barrage of statements against Harris started during Thursday's debate, after she criticized Biden for opposing busing that integrated public schools. Harris was widely seen as winning the second of the back-to-back Democratic debates in Miami.

She was born in Oakland, California, to an Indian mother and Jamaican father.

After the clash with Biden, a Twitter account under the name Ali Alexander posted, "Kamala Harris is implying she is descended from American Black Slaves. She's not. She comes from Jamaican Slave Owners. That's fine. She's not an American Black. Period."

Donald Trump Jr. retweeted another remark From Alexander, but then deleted it.

Behavioral scientist Caroline Orr noted this week that a number of Twitter accounts seemed to be posting the same message in lockstep, a sign of a coordinated influence campaign.

"What a weird coincidence that a group of accounts, starting with Ali, decided to tweet the exact same thing (verbatim) about Kamala Harris within minutes of each other tonight," she tweeted.

CORRECTION (July 1, 2019, 1 p.m.): A previous version of this article misstated which tweet by Ali Alexander was tweeted and then deleted by Donald Trump Jr. Trump retweeted and then deleted a post that began, “Kamala Harris is *not* an American Black. She is half Indian and half Jamaican." He did not retweet a similar post that began “Kamala Harris is implying she is descended from American Black Slaves. She's not.”