WATCH: In Show Of Party Unity, Bernie Sanders Endorses Hillary Clinton

The lingering chasm between presumptive Democratic presidential nominee Hillary Clinton and her chief primary rival was bridged Tuesday, with Sen. Bernie Sanders teaming up with Clinton at a campaign event, where he formally endorsed Clinton's bid for the White House.

"Secretary Clinton has won the Democratic nominating process, and I congratulate her for that," Sanders said. "She will be the Democratic nominee for president and I intend to do everything I can to make certain she will be the next president of the United States.

"I have come here today not to talk about the past but to focus on the future. That future will be shaped more by what happens on Nov. 8 in voting booths across our nation than by any other event in the world. I have come here to make it as clear as possible as to why I am endorsing Hillary Clinton and why she must become our next president."

The Sanders endorsement ends a lengthy — and awkward — period in which many were wondering if and how he would back Clinton. Five weeks ago, Clinton, the Democratic Party's presumptive nominee, became the first woman in American history to secure enough delegates to clinch the nomination to head the ticket of a major party.

Before the event kicked off, NPR's Tamara Keith noted feuding chants of "Hillary" and "Bernie" coming from the crowd. There was also a younger Sanders supporter shouting "Never Hillary," as well as mentions of the FBI investigation into Clinton's email server, while sitting next to older women supporting Clinton, who appeared to be getting increasingly tense.

But Democrats now get a chance to turn the page on a contentious primary campaign and promote a party that is unified, just days before the Republicans are set to kick off their own convention in Cleveland next week.

New Hampshire is a state Sanders won handily during the primary — by more than 20 points — and catapulted his bid for the nomination into a robust campaign that challenged Clinton longer than most had predicted.

The win helped Sanders raise massive amounts of money, more than the Clinton juggernaut — $225 million to Clinton's $210 million through the end of May. Sanders also outspent Clinton by $23 million ($216 million to $193 million).

Sanders rode a wave of massive rallies that filled college arenas, where he championed issues, like beating back Wall Street's influence and overcoming income equality, which energize the liberal wing of the Democratic base, especially young voters and white liberals.

As NPR's Tamara Keith reported Monday, Democrats gathered in Orlando, Fla., this past weekend to hash out planks of the party's platform. It now includes pushing for tuition-free state college, a $15 minimum wage, limits on fracking and other items Sanders campaigned on.

Since becoming the presumptive nominee, Clinton has campaigned alongside President Obama and Massachusetts Sen. Elizabeth Warren, both of whom are wildly popular among Democrats. She has also warned a Trump presidency would push the country in the wrong direction.

In 2008, it took Clinton only four days to come out in support of Obama after their long primary battle. Sanders, by contrast, has held out about a month from the end of the primary season. Both Clinton and Sanders huddled in Washington last month, and NPR's Tamara Keith has reported that both camps have maintained continual contact since that meeting.

Clinton's appearance alongside Sanders could do a lot to assuage his supporters who may remain on the fence about supporting her candidacy, especially among young voters. Democrats head to their party convention in Philadelphia, where Clinton will be formally nominated later this month.

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