Former President Barack Obama endorsed Joe Biden, his former vice president, in a video released Tuesday.

Why it matters: Obama, following in the footsteps of other recent former presidents, chose to let the crowded Democratic primary process play out and not offer an endorsement until voters chose their presumptive nominee.

Biden leaned heavily on his strong relationship with Obama and his record as vice president throughout the primary race while still acknowledging that he needed to "earn" Obama's endorsement.

Obama's endorsement comes one day after Biden's final rival in the race, Bernie Sanders, offered his own endorsement.

Highlights from the endorsement:

"Choosing Joe to be my vice president was one of the best decisions I ever made, and he became a close friend. And I believe Joe has all the qualities we need in a president right now. He’s someone whose own life has taught him how to persevere; how to bounce back when you’ve been knocked down."

"Joe helped me manage H1N1 and prevent the Ebola epidemic from becoming the type of pandemic we’re seeing now. He helped me restore America’s standing and leadership in the world on the other threats of our time, like nuclear proliferation and climate change. Joe has the character and the experience to guide us through one of our darkest times and heal us through a long recovery."

"Each of our candidates were talented and decent, with a track record of accomplishment, smart ideas, and serious visions for the future. And that’s certainly true of the candidate who made it farther than any other – Bernie Sanders. Bernie’s an American original – a man who has devoted his life to giving voice to working people’s hopes, dreams, and frustrations. He and I haven’t always agreed on everything, but we’ve always shared a conviction that we have to make America a fairer, more just, more equitable society."

"This crisis has reminded us that government matters. It’s reminded us that good government matters. That facts and science matter. That the rule of law matters. That having leaders who are informed, and honest, and seek to bring people together rather than drive them apart – those kind of leaders matter."

The big picture: Former top Obama adviser David Axelrod told Politico last year that a lengthy endorsement process shouldn't be taken as a dig towards Biden, who he said remains "genuinely friends" with the former president.

"The custom for former presidents is not to endorse presidents. The expectation that he would, I find kind of baffling."

The backdrop: The pair were initially competitors in the 2008 presidential race.

Obama said he picked Biden to be his running mate because he wanted someone "with a little gray in their hair," according to the New York Times.

Images of their friendship — like enjoying ice cream and laughing together — eventually became symbols of the Obama administration.

The complexities of their relationship emerged when Biden pondered a 2016 challenge to Hillary Clinton, which Obama did not encourage, per the Washington Post.

Go deeper: Read Obama's full endorsement