"It's about time we start unifying as a party and begin the work to beat Donald Trump and, frankly, save our nation, humanity, address our common cause and our common challenges," Booker told "CBS This Morning."

Booker's support adds to the already significant consolidation of former Democratic White House hopefuls and party leaders around Biden, and comes one day before the next slate of state primaries in Idaho, Michigan, Mississippi, Missouri, North Dakota and Washington.

Booker, who dropped out of the nominating contest in January after centering his campaign on themes of love and justice, was one of several candidates who struggled to emerge as an alternative to Biden in what began as a historically diverse and crowded Democratic field.

As the primary fight intensified, Booker frequently challenged Biden on matters of race, blasting the former vice president for statements he made about working with segregationist lawmakers in the Senate and arguing that Biden was ill-equipped to effectively discuss America's centuries-old racial wounds.

Booker also expressed concerns about Biden's gaffe-prone oratorical style and unsteady debate performances, remarking that Democrats "have to have a nominee that's up to this challenge" and asserting that voters were worried about his "ability to carry the ball all the way across the end line without fumbling."

Downplaying his previous criticisms of his former competitor, Booker insisted Monday that "I love Joe Biden," adding that he was "enthusiastic about this decision" to endorse.

"As I look at him, I know factually from talking to him that some of my biggest issues — like criminal justice reform, like racial justice, like economic justice — that he is going to be a strong leader on that and can actually pull the country together, the kinds of coalitions we need, to actually make progress in those areas," Booker said.

Booker's endorsement reflects the current realities of the primary race, which has effectively narrowed to Biden and Sanders, a self-identified democratic socialist who many in the party fear is too left-wing to head up the ticket in November and could negatively impact down-ballot Democratic candidates in House and Senate races.

"Bernie's my friend. I have a lot of respect for him and have worked with him in Washington, D.C." Booker said. "I just want us to get beyond pointing fingers at each other and trying to tear each other down. We can't tolerate that right now. The threat is in the White House."

Sanders and his supporters have accused senior members of the Democratic establishment of lining up to thwart his campaign in the aftermath of Biden's impressive performance in last week's Super Tuesday primaries — a charge echoed by the president as he seeks to sow division among Democrats ahead of the general election.