The Democratic Party's top congressional leaders have joined the chorus of members throwing their support behind Vice-President Kamala Harris, formally endorsing her presidential bid together on Tuesday.

Sen. Chuck Schumer and Rep. Hakeem Jeffries, both from New York, said they were backing Harris as the candidate best positioned to lead the party ticket.

"We all know that Vice-President Harris has a tremendous record to run on and now begins the next chapter in our quest to make sure Donald Trump does not become president," Schumer said, addressing reporters in Washington on Tuesday.

WATCH | Harris makes her case against Trump: 

Kamala Harris lays out her case against Donald Trump as money, endorsements roll in

High-profile Democrats, including Nancy Pelosi, have announced their support for Kamala Harris as the presidential nominee, and the party pulled in $81 million in donations after Joe Biden dropped out.

Schumer, the Senate majority leader, and Jeffries, minority leader in the House of Representatives, were among the party brass who stopped short of immediately endorsing Harris's run after dozens of Democratic governors, donors, lawmakers and potential opponents made a mad dash to do so after she launched her campaign with President Joe Biden's approval on Sunday.

Nancy Pelosi did not endorse Harris until later Monday, while former president Barack Obama has not yet done so.

Political scientists and historians suggested heavy-hitters might have held off on backing Harris to avoid creating the impression that the party was simply appointing Harris as their candidate, instead respecting her wish to "earn and win" her nomination under party rules.

Speaking Tuesday, Schumer confirmed that was the case.

"When I spoke with her Sunday, she said she wanted the opportunity to win the nomination on her own and to do so from the grassroots up, not top down," Schumer told reporters. "We deeply respected that, Hakeem and I. She said she would work to earn the support of our party and, boy, has she done so in quick order."

Jeffries added that Harris is "ready, willing and able to lead" the party.

Riding a tsunami of party support, Harris has already locked up enough backing from Democratic delegates to win her party's nomination to challenge Trump, the Republican nominee, at a roll call vote expected in early August. She formally launched her campaign on Sunday with the endorsement of Biden, who bowed out of the race that afternoon.

Harris travelled to Milwaukee, Wis., on Tuesday to hold her first presidential campaign rally in one of the most crucial battleground states of the election. 

For more than 30 years, the Midwestern state was a brick in the "Blue Wall" — a term for states that reliably went to the Democrats from the '90s into the early 2010s.

The winning streak came to an end when Donald Trump won the state back in 2016, helping him secure his marginal victory over Hillary Clinton. Biden took back Wisconsin in 2020, but only won by less than one percentage point.

"The path to the White House goes through Wisconsin," Harris said during her rally Tuesday.

The vice-president had the visit scheduled before Biden dropped out of the race, but it takes on new significance after Harris looks to mount a campaign and restore a sense of unity and control to the party after Biden's disastrous debate performance on June 27 derailed his campaign.

Biden is returning to the White House on Tuesday from his beach house in Delaware after recovering from COVID-19. He will address the nation for the first time since ending his campaign at 8 p.m. ET on Wednesday, just hours after Israeli Prime Minister Benjamin Netanyahu addresses U.S. Congress.

Schumer and Jeffries praised Biden's decision to abandon his own bid, with Schumer saying the "selfless decision" gave the party "the opportunity to unite behind a new nominee."