Sen. Cory Booker Cory Anthony BookerDHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility Black Voters Matter Fund deploying voter outreach caravans in 12 states to drive turnout MORE (D-N.J.) announced his support for former Vice President Joe Biden Joe BidenCast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response Biden tells CNN town hall that he has benefited from white privilege MORE's presidential campaign early Monday, adding to Biden's list of endorsements from his former primary opponents.

"The answer to hatred & division is to reignite our spirit of common purpose," Booker, who ended his own presidential campaign in January, said in a tweet.

"@JoeBiden won’t only win - he’ll show there's more that unites us than divides us," the senator said, adding that Biden will "restore honor to the Oval Office and tackle our most pressing challenges."

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"That’s why I’m proud to endorse Joe," he said.

The answer to hatred & division is to reignite our spirit of common purpose.@JoeBiden won’t only win - he’ll

show there's more that unites us than divides us.



He’ll restore honor to the Oval Office and tackle our most pressing challenges.



That’s why I’m proud to endorse Joe. pic.twitter.com/RcsnZs5mfQ — Cory Booker (@CoryBooker) March 9, 2020

Biden has added a slew of endorsements since an impressive showing on Super Tuesday last week, including one from Sen. Kamala Harris Kamala HarrisScott Walker helping to prep Pence for debate against Harris: report California family frustrated that governor, Harris used fire-damaged property for 'photo opportunity' Moderna releases coronavirus vaccine trial plan as enrollment pushes toward 30,000 MORE (Calif.), another former rival for the Democratic presidential nomination.

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Sen. Amy Klobuchar Amy KlobucharEPA delivers win for ethanol industry angered by waivers to refiners It's time for newspapers to stop endorsing presidential candidates Biden marks anniversary of the Violence Against Women Act, knocks Trump and McConnell MORE (D-Minn.) and former South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegBogeymen of the far left deserve a place in any Biden administration Overnight Defense: Woodward book causes new firestorm | Book says Trump lashed out at generals, told Woodward about secret weapons system | US withdrawing thousands of troops from Iraq A socially and environmentally just way to fight climate change MORE endorsed Biden after ending their 2020 campaigns shortly before Super Tuesday. The support from those fellow moderate candidates may have contributed to Biden’s surge in the 15 states in which ballots were cast last Tuesday. Biden himself credited Klobuchar for cinching his win in Minnesota.

Former Texas Rep. Beto O’Rourke (D) also endorsed Biden before Super Tuesday.

Sen. Elizabeth Warren Elizabeth WarrenWarren, Schumer introduce plan for next president to cancel ,000 in student debt The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon No new taxes for the ultra rich — fix bad tax policy instead MORE (D-Mass.), a progressive candidate who ended her campaign after Super Tuesday, has said she will not immediately endorse a candidate.

Biden holds a slight lead in delegates over Sen. Bernie Sanders Bernie SandersMcConnell accuses Democrats of sowing division by 'downplaying progress' on election security The Hill's Campaign Report: Arizona shifts towards Biden | Biden prepares for drive-in town hall | New Biden ad targets Latino voters Why Democrats must confront extreme left wing incitement to violence MORE (I-Vt.). The two candidates will face off in six contests on Tuesday.

--Rebecca Klar contributed to this report, which was last updated at 7:52 a.m.