Vice President Kamala Harris is marching to the Democratic nomination as broad swaths of the party — including potential rivals, lawmakers, governors, influential labor and advocacy groups and more — line up behind her bid to take on Donald Trump.

No credible challenger had emerged by late Monday morning, nearly a full day after President Joe Biden had announced his exit from the race and his endorsement of his vice president.

And the party’s best-known governors, several of whom had been seen as potential challengers, announced their support for Harris — making clear that the biggest remaining question about the 2024 Democratic ticket is who Harris will choose as her running mate.

Four governors of must-win Midwestern states — Michigan’s Gretchen Whitmer, Minnesota’s Tim Walz, Wisconsin’s Tony Evers and Illinois’ JB Pritzker — endorsed Harris on Monday. They followed Sunday endorsements of Harris from Kentucky’s Andy Beshear, North Carolina’s Roy Cooper, California’s Gavin Newsom and Pennsylvania’s Josh Shapiro. Many of those governors could be considered for the party’s vice presidential nomination.

In her first half-day as a candidate, Harris raised $49.6 million in online donations, campaign spokeswoman Lauren Hitt said — a huge haul that underscored grassroots enthusiasm for a shake-up to the Democratic 2024 ticket. Democratic donation-processing site ActBlue called it “the biggest fundraising day of the 2024 cycle.”

Meanwhile, the cascade of endorsements for Harris’ candidacy that had begun Sunday afternoon was accelerating on Capitol Hill. Harris has the support of more than 30 Democratic senators and more than 80 House members — numbers that had grown rapidly throughout Monday morning.

She also has the support of the political arms of the Congressional Black Caucus, Congressional Hispanic Caucus and Congressional Progressive Caucus, as well as two key labor unions, Service Employees International Union and the American Federation of Teachers.

And several state delegations to next month’s Democratic National Convention — Tennessee, North Carolina, South Carolina, Louisiana, New Hampshire and Maryland — announced that they are backing Harris.

Support for the vice president came across the party’s ideological spectrum — from moderate populists, including Ohio Sen. Sherrod Brown, one of the most endangered Democratic incumbents on the ballot this fall, to progressives, including Massachusetts Sen. Elizabeth Warren and New York Rep. Alexandria Ocasio-Cortez.

Democratic congressional leaders had remained quiet so far — but there were signs that could soon change. Massachusetts Rep. Katherine Clark and California Rep. Pete Aguilar, the second- and third-ranking House Democrats, endorsed Harris on Monday morning.

The hour-by-hour endorsements of Harris from Democratic governors, senators, Cabinet officials and state delegations is unfolding by design, with the hope of reaching a majority of delegates by Wednesday, two people familiar with the process tell CNN.

“It’s a coordinated drumbeat,” a senior Democratic aide working on the effort said. “That sound Democrats hear is the party uniting around the vice president.”

How Harris and her allies mobilized

Joe Biden’s 1:46 p.m. ET Sunday announcement that he would not seek a second term ignited a frenetic push by Harris to consolidate the support of a party that had been in crisis in the weeks since the president’s dismal performance during his June 27 debate with former President Donald Trump.

Harris knew what Biden had decided: She’d had multiple phone calls with Biden on Sunday, a person familiar with the matter said. Once the announcement came, Harris — wearing a hoodie from her alma mater, Howard University, workout sweats and sneakers — made more than 100 phone calls over 10 hours.

Alongside her family and staff, the vice president’s calls included lawmakers, governors and leaders of influential labor, advocacy and civil rights groups.

Those calls included former Presidents Barack Obama and Bill Clinton, as well as former Secretary of State Hillary Clinton. The Clintons, in a statement Sunday, endorsed Harris; Obama did not, deferring to the party’s process.

Harris also called her pastor, Amos Brown III, who, along with his wife, prayed over her, the source said. She ate pizza with anchovies — Harris’ go-to topping — for dinner.

In those phone calls, Harris made clear that while she was grateful for Biden’s endorsement, she planned to earn the Democratic nomination in her own right. That echoes the statement she released following Biden’s announcement to step aside.

“I am honored to have the President’s endorsement and my intention is to earn and win this nomination,” she wrote.

Harris’ supporters were also mobilizing.

The group Win With Black Women periodically holds Zoom calls — but the one that took place Sunday evening had a different tone, with 44,000 people joining, according to its leaders.

Longtime Democratic operative Donna Brazile said that she was in the process of gathering delegates to support Harris. “I need all of you to sign your delegate pledge forms now,” Brazile said on the call. She said voter registration and fundraising will be key in the days ahead.

Washington, DC, Mayor Muriel Bowser also spoke on the call.

“I know what it’s like to be in the crosshairs of Donald Trump,” she said. “We have to defend our sister.”

Former Congressional Black Caucus Chairwoman Joyce Beatty and Texas Rep. Jasmine Crockett were also among the speakers.

No serious challenger materializes yet

Though some Democrats have held off on announcing endorsements, no serious challenger has emerged to take on Harris for the nomination ahead of the Democratic National Convention, which starts August 19 in Chicago.

Any challenge might need to materialize even faster: Prior to Biden’s departure from the race, the party had set up a virtual roll call to begin the first week of August. There are no signs at this point it intends to abandon those plans.

Manchin, who had left the party earlier this year and is not seeking reelection, said Monday he will not rejoin the party and seek its nomination.

CNN has previously reported the West Virginia senator was considering re-registering as a Democrat to throw his hat in the ring. But in an interview with CBS News on Monday, Manchin said he will not be a candidate.

“I could not believe that there was not going to be a primary process or a mini process. Other countries do it,” Manchin said, adding that he believes Harris is too liberal but could be forced to the middle if she faces a challenge.

New York City Democratic Mayor Eric Adams announced his support for Harris in an interview with MSNBC on Monday, reversing course just hours after he told CNN, “there’s a process and we’re going to follow that process,” to determine the party’s nominee.

“We need real, clear, leadership, and she understands it,” Adams told MSNBC. “She was in the position of looking over the border issue, so she understands some of the things that we need to do.”

And he offered a stirring endorsement of Harris’ fitness to lead the ticket, urging advisers to “let her be her.”

Running mate jockeying begins

As of mid-morning Monday, as the swell of support for Harris continued to build, the biggest question might have been who she will choose as a running mate.

Democratic lawyers are beginning their work conducting a deep, yet truncated, vetting process for potential vice presidential hopefuls, two people familiar with the matter told CNN, with siloed teams being established for the leading prospective candidates.

Cooper, Shapiro and Arizona Sen. Mark Kelly are among the Democrats who have been asked to submit information about their finances, family histories and other personal details, two people familiar with the process said. They are part of a group that includes about 10 names, nearly all of whom are elected officials.

A handful of Democratic lawyers, including those who have worked on vice presidential vetting processes in the past, are involved in this effort.

The audition process is also playing out in public, with Cooper and Beshear appearing on MSNBC’s “Morning Joe” on Monday — with the intent that Harris was watching. An aide said she caught at least part of the conversations.

Beshear, the two-term Kentucky governor, announced his support for Harris — and said he is open to joining Harris as her potential running mate, noting it’s “flattering to be a part” of the conversation about the vice-presidential nomination.

He also offered a window into how he’d play the traditional attack-dog role of a running mate. At multiple points in the interview, Beshear attacked Republican vice presidential nominee JD Vance, who has family ties to Beshear’s home state of Kentucky.

“Let me just tell you that JD Vance ain’t from here,” Beshear said, referring to his home state, taking issue with how Vance described Appalachia in his best-selling memoir “Hillbilly Elegy.”

Beshear also attacked Vance for past comments expressing support for strict restrictions to abortion access, while touting Harris’ record of supporting protections for reproductive health care.

“JD Vance calls pregnancy arising from rape ‘inconvenient,’” Beshear said. “No, it’s just plain wrong. He suggests that women should stay in abusive relationships. Now listen, a domestic abuser isn’t a man, he’s a monster, and no one should support anyone having to stay in those relationships.”

Cooper, the North Carolina governor who endorsed Harris on Sunday, also appeared on MSNBC on Monday, but deflected questions about whether he would be open to becoming her running mate.

“I think it’s really important that we do keep the focus on her this week. The vice-presidential conversation needs to occur later,” Cooper said. “I want to make sure that Kamala Harris wins. I’m going to work for her all over this country and do what I can to make sure we stop Donald Trump.”

This story and headline have been updated with additional reporting.

CNN’s Jeff Zeleny, Ebony Davis, Aaron Pellish, MJ Lee, DJ Judd and Eva McKend contributed to this report.