Kamala Harris seemed to prove in Miami in June that she was ready to take the offensive against 2020 Democratic frontrunner Joe Biden.

So after Biden referred to the 54-year-old U.S. senator as “kid” on Wednesday, it probably didn’t seem like an accident to some when Harris referred to the 76-year-old former vice president as “Senator” at least twice during Wednesday’s debate in Detroit.

KAMALA HARRIS 'GOT IT WRONG' IN 'SAD' ATTACK ON BIDEN, FORMER US SENATOR SAYS

"In response to Senator Biden about the Affordable Care Act, it’s important you understand our 'Medicare for all' plan has actually by the architect of the Obama Affordable Care Act been described as one of the most effective ways to bring health care to all,” Harris said at one point during the debate.

“Senator Biden, your plan will keep and allow insurance companies to remain in status quo, doing business as usual," Harris said later.

The references to Biden’s days representing Delaware in the U.S. Senate appeared to irk Andrew Bates, the “rapid response” director for Biden’s campaign.

“Fact check: @JoeBiden is not a ‘Senator,’” Bates wrote on Twitter.

Prior to the debate, Biden had greeted Harris on the debate stage in Detroit.

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“Go easy on me, kid,” Biden said, in an apparent reference to the clash between the candidates in Miami last month.

“Kid?” came the one-word response from Ian Sams, Harris’ national press secretary.

In June, Harris aggressively went after Biden on the debate stage in Miami, criticizing him for comments he had made about his ability to find common ground during the 1970s with segregationist senators with whom he disagreed, and over his opposition decades ago to federally mandated school busing.

The impact of Harris' move was almost instant: Biden lost some of his lead in the polls while Harris' numbers climbed.

Fox News' Joseph A. Wulfsohn and Paul Steinhauser contributed to this story.