Former Vice President Joe Biden greeted Sen. Kamala Harris (D-CA), one of his most vocal critics, humorously at the start of the second Democrat presidential debate on Wednesday. “Go easy on me, kid,” Biden said audibly when shaking hands with Harris on stage before the start of the debate in Detroit, Michigan.

The humorous moment underscores weeks of tension between the two politicians. Harris surprised many at the first debate last month when she confronted Biden over his praise for two segregationist Democrats. Biden had invoked the men, Sens. James Eastland (D-MS) and Herman Talmadge (D-GA), repeatedly on the campaign trail while touting his ability to forge “consensus” in Congress.

“I agree with you when you commit yourself to the importance of finding common ground,” Harris said, “but I also believe … 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.”

Harris was quick to point out that both Talmadge and Eastland were allies in Biden’s crusade against busing to integrate public schools.

“It was not only that, but you also worked with them to oppose busing,” Harris said. “There was a little girl in California who was part of the second class to integrate her public schools and she was bussed to school every day. That little girl was me. So I will tell you that on this subject, it cannot be an intellectual debate. … We have to take it seriously.”

The attack left Biden reeling to respond. The former vice president accused Harris of mischaracterizing his record. Instead of offering proof, however, the 76-year-old frontrunner only jumbled his position on busing and falsely claimed to have never praised racists.

In the intervening weeks since the altercation, Harris and Biden have traded barbs on the campaign trail and on social media.