Presumptive Democrat nominee Joe Biden has selected Sen. Kamala Harris (D-CA) to be his running mate, making her the first black woman on a major White House ticket, the former vice president announced on social media Tuesday afternoon.

“I have the great honor to announce that I’ve picked @KamalaHarris — a fearless fighter for the little guy, and one of the country’s finest public servants — as my running mate,” Biden wrote on Twitter.

The White House candidate continued: “Back when Kamala was Attorney General, she worked closely with Beau. I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse. I was proud then, and I’m proud now to have her as my partner in this campaign.”

In a statement after her selection, Harris tweeted: “[email protected] can unify the American people because he’s spent his life fighting for us. And as president, he’ll build an America that lives up to our ideals. I’m honored to join him as our party’s nominee for Vice President, and do what it takes to make him our Commander-in-Chief.”

Following the announcement, the Biden campaign said both candidates will speak Wednesday in Wilmington, Delaware, “on working together to restore the soul of the nation and fight for working families to move the country forward.”

Harris ended her own bid for the White House in December amid dismal poll numbers and reported turmoil in her campaign. Although the California Democrat launched her campaign with much fanfare, her failed path to the White House never generated support akin to top tier candidates such as Sens. Elizabeth Warren (D-MA) and Sen. Bernie Sanders (I-VT), and of course, her running mate, Biden.

President Donald Trump’s re-elected campaign swiftly responded to Biden’s selection of Harris, branding the pair: “Slow Joe and Phony Kamala.”

“Kamala Harris ran for president by rushing to the radical left, embracing Bernie’s plan for socialized medicine, calling for trillions in new taxes, attacking Joe Biden for racist policies,” the Trump campaign said in a video tweeted by President Trump. “They smartly spotted a phony — but not Joe Biden. He’s not that smart,” the ad continues, before adding Biden “is handing over the reins to Kamala” if the two win in November.

“Slow Joe and Phony Kamala: Perfect together, wrong for America,” the ad concludes.

Biden and Harris famously clashed in heated confrontations over the issue of busing to desegregate public schools during the Democrat presidential debates.

As Breitbart News reported:

[One of the] altercation[s] was initiated by CNN when the debate’s moderators asked Harris if her position against federally mandated busing was the same as the one touted by Biden. Harris began her response by saying it was “simply false” to claim she and the former vice president stood on the same side of the issue, before moving to broader denouncement of Biden and his recent praise of segregationists.

Harris said that on the topic she and Biden could not “be further apart,” adding the former vice president was still refusing to acknowledge his past. The attack echoes the one Harris launched at the first debate when she confronted Biden for praising the “civility” of two segregationists Democrats, the late Sens. James Eastland (D-MS) and Herman Talmadge (D-GA). Biden had invoked the men, who dedicated their careers to halting the progress of civil rights, while touting on the campaign trail his ability to forge legislative “consensus.”

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The rebuke left Biden reeling to respond. The former vice president accused Harris of mischaracterizing his record, but rather than offering proof the 76-year-old frontrunner only muddled his stance on busing and falsely claimed to have never praised racists.

Harris, born in Oakland to an Indian mother and Jamaican father, was the second black woman to be elected in 2016 to the Senate.

Harris’ record as California attorney general and district attorney in San Francisco was heavily scrutinized during the Democratic primary and turned off some liberals and younger Black voters who saw her as out of step on issues of systemic racism in the legal system and police brutality. She tried to strike a balance on these issues, declaring herself a “progressive prosecutor” who backs law enforcement reforms.

Biden, who spent eight years as President Barack Obama’s vice president, has spent months weighing who would fill that same role in his White House. He pledged in March to select a woman as his vice president, easing frustration among Democrats that the presidential race would center on two white men in their 70s.

The Associated Press contributed to this report.