Kamala Harris is locking down support. Any Democrat who wants to rip the nomination from her faces a steep climb.

• Vice President Kamala Harris moved quickly to lock down major support for a 2024 presidential bid.
• President Joe Biden endorsed her Sunday after his abrupt announcement that he was exiting the race.
• Harris already has access to a $91 million war chest, among other advantages.

Big-name Democrats and outside groups moved quickly on Sunday to try to help Vice President Kamala Harris lock down the party's nomination following President Joe Biden's seismic decision to drop out of the 2024 race.

Following Biden's endorsement , the president's reelection campaign committee rebranded itself to " Harris for President ," handing her the keys to a $91 million war chest. Other Biden-linked groups changed their affiliation as well. Unless a wealthy Democrat cut their own campaign a giant check, it's unlikely anyone could match that massive amount of money right out of the gate.

It remains to be seen whether Harris will avoid a high-profile challenger . Biden can direct his delegates to support her, but officially the group of more than 4,000 Democrats is not permanently bound to his wishes.

Within a few hours, Harris' list of supporters included some of the biggest names in the Democratic Party — posing another sizable bulwark to any challenger. Among the vice president's endorsements are former President Bill Clinton and EMILY's list, a group seeking to elect women in favor of abortion rights.

"Now is the time to support Kamala Harris and fight with everything we've got to elect her," Clinton said in a joint statement with former Secretary of State Hillary Clinton. "America's future depends on it."

The Congressional Black Caucus' political arm, which had remained behind Biden even as more Democrats tried to drive him out of the race, also lined up behind the vice president. Rep. Nanette D. Barragán of California, the chair of the Congressional Hispanic Caucus, also endorsed Harris.

Numerous powerful women have lined up behind Harris. In addition to Hillary Clinton, the first woman to become a major US party's presidential nominee, Harris has support from Sen. Patty Murray of Washington, a member of Senate leadership who is third in the line of succession to the presidency.

"I am behind Kamala Harris one-hundred percent — she is exactly the woman we need to prosecute the case against Donald Trump, save American democracy, lead the fight to restore abortion rights, and build an economy that puts working people — not billionaires — first," Murray, who is also president pro tempore of the Senate, said in a statement.

Not everyone was quick to line up behind her. Former President Barack Obama indicated that he supported an open-primary process. It remains to be seen how such a process might unfold since the Democratic primaries have concluded. The party's national convention is also set to start in less than a month in Chicago.

"We will be navigating uncharted waters in the days ahead. But I have extraordinary confidence that the leaders of our party will be able to create a process from which an outstanding nominee emerges," Obama said in his lengthy statement that praised Biden's decision to step aside.

A source familiar with Obama's thinking said the former president thought it best to remain on the sidelines so he could help bring the party together in the event of hard feelings after the process.

"Just like he did in 2020 once Joe Biden earned the nomination, President Obama believes he will be uniquely positioned to help unite the party once we have a nominee, lift up that candidate, and do everything he can to get that candidate elected in November," the unnamed source told NBC News .

A fellow Californian, former House Speaker Nancy Pelosi, also didn't address Harris' future in her statement. Pelosi was widely perceived as helping to orchestrate the push that led Biden to bow out.

Leaders of the AFL-CIO, part of a labor wing that has been a staunch Biden ally, repeated their past support of the Biden-Harris ticket but too stopped short of a full endorsement of Harris.

Democrats' gamble has shaken up the race, but former President Donald Trump could still reclaim the White House. No one has ever seen the type of 100-day sprint that will now take place before Election Day.

Beyond seeking to upstage the first female vice president, other ambitious Democrats would have to raise their national profile in a way Harris does not. Such an introduction is an even greater obstacle considering that Trump is perhaps the best-known figure in modern politics. While no Democrat would openly acknowledge it, if Harris were to falter, it could open up the 2028 race to a greater degree. In contrast, besting Harris and falling to Trump would stain a rising star's status.

The prospect of Harris' nomination is far from a political panacea for nervous Democrats. Republicans have made it clear they will try to tie her candidacy to the least popular parts of Biden's record, particularly on immigration.

One of the biggest sources to watch in the days ahead will be the Democratic National Committee. As leader of his party, Biden pushed the DNC to rubber stamp his plan to shake up the primary calendar. Democrats also didn't hold any primary debates, as Biden avoided any major challengers.

The DNC was plowing ahead with a controversial plan to name Biden the nominee before the August convention. As of now, the virtual vote was not expected to occur before August 1. If the virtual vote moves forward, ambitious Democrats will face an even tighter window to organize opposition to Harris' nomination.