The exchange surfaced after Trump Jr. tweeted the question: "Why is @KamalaHarris the only person that laughs at her jokes ... always way to [sic] long and way too hard?" He added that she was the "most disingenuous person in politics ... after Hillary," a reference to his father's former opponent, Hillary Clinton.
Harris responded with an apparent attack on his father. "You wouldn’t know a joke if one raised you," she tweeted.
Trump Jr. shot back with a comment on her poll numbers. "Based on your tanking poll numbers, what’s definitely a joke is your entire campaign Yikes!" he tweeted.
According to a Fox News poll from Oct. 6-8, Harris grabbed 15 percent of national Democratic primary voters' support, placing her fourth behind former Vice President Joe Biden, Sen. Elizabeth Warren, D-Mass., and Sen. Bernie Sanders, I-Vt.
Harris recently faced criticism for calling on Twitter to suspend President Trump's account. The senator sent a letter to Twitter CEO Jack Dorsey, accusing the president of violating the company's terms of service.
"I believe the president's recent tweets rise to the level that Twitter should consider suspending his account," she said. "When this kind of abuse is being spewed from the most powerful office in the United States, the stakes are too high to do nothing."