The decision by Sen. Kamala Harris to attack former Vice President Joe Biden over school busing during Thursday's Democratic Party debate could hurt the party heading into 2020, according to Dennis Kucinich.

"Joe Biden's record is fair game," the two-time Democratic presidential candidate said Friday on Fox News' "The Ingraham Angle." "But if you divide Democrats on race, you lose."

"You divide and Trump conquers," added Kucinich, 72, a former mayor of Cleveland who later served in the U.S. House from 1997 to 2013.

"If you want African-Americans to vote, have a plan -- address racial disparity, wealth, wages, health. Talk about working-poor families. Look at the crime and the murder rate in black communities and how people are treated by the police. These are issues that will motivate people.

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"But if you just use it on race in kind of a personal attack, Democrats are going to lose."

Kucinich said he believed, however, that Biden remained a formidable candidate.

"He seems to have strong support in the black community," he said. "I don't think that will disintegrate."

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During the debate, Harris appeared to inflict serious damage on Biden after she pointed out that Biden’s work with segregationist senators had a human cost – including to her.

“I also believe — and it is personal — and it was actually very 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 said.

“You worked with them to oppose busing,” Harris added, referring to efforts to limit orders for school desegregation by busing.

In an emotional moment, she told her own story of being bused as a young girl in California.

Fox News' Lukas Mikelionis contributed to this report.