AMNA NAWAZ: Welcome to the "News Hour."

Vice President Kamala Harris is entering# uncharted territory after President Joe## Biden announced his withdrawal from the# presidential race yesterday.

One day later,## Harris is already the favorite to win the# Democratic Party nomination for president.

Laura Barron-Lopez has the latest.

(CHEERING) (APPLAUSE) Vice President Harris arrived at# her campaign office in Wilmington,## Delaware, this afternoon ahead of her first# campaign event as a presidential candidate.

JOE BIDEN, President of the United States:# With the COVID -- excuse me -- with... LAURA BARRON-LOPEZ: It comes 25 days# after President Biden's disastrous## debate performance that raised# questions about his ability to run.

REP. JAMIE RASKIN (D-MD): There are# very honest and serious and rigorous## conversations taking place# at every level of our party.

LAURA BARRON-LOPEZ: For weeks, the# president faced mounting pressure## from allies in his own party to end his campaign.

JOE BIDEN: I am running and going to win again.

LAURA BARRON-LOPEZ: But he# insisted that he was all in## and almost nothing could convince him to drop out.

JOE BIDEN: If the lord almighty# came down and said, "Joe,## get out of the race," I would get out of the# race.

The lord almighty is n.. LAURA BARRON-LOPEZ: Then, during# a weekend of isolation at his## home in Delaware with a COVID diagnosis,# President Biden announced his decision.

He wrote in a letter posted on# the social media site X Sunday:## "It has been the greatest honor of# my life to serve as your president,## but it is in the best interest of my party# and the country for me to stand down."

Shortly after, he threw his full support behind# Harris.

Top Democrats like the Obamas, the## Clintons, and leaders in Congress praised Biden's# decision to drop out.

Even former Vice President## Mike Pence applauded the move, writing on X today:# "President Joe Biden made the right decision for## our country, and I thank him for putting the# interests of our nation ahead of his own."

Harris herself praised the president# at the White House this morning.

KAMALA HARRIS, Vice President of the United States# (D) and U.S. Presidential Candidate: Every day,## our president, Joe Biden, fights for# the American people, and we are deeply,## deeply grateful for his service to our nation.

LAURA BARRON-LOPEZ: Many Democrats quickly# united behind Harris.

In its first 24 hours,## Harris' campaign racked up# $81 million in donations,## the highest 24-hour raise, her team# said, of any candidate in history.

Some who were seen as possible# competitors to Harris lined up behind her.

GOV.

ANDY BESHEAR (D-KY): I'm excited# to fully endorse Vice President Harris.

LAURA BARRON-LOPEZ: Kentucky Governor Andy# Beshear gave his backing this morning,## but sidestepped questions about# whether he'd serve as her running mate.

GOV.

ANDY BESHEAR: The only way I would# consider something other than this current## job is if I believed I could further# help my people and to help this country.

LAURA BARRON-LOPEZ: North Carolina Governor# Roy Cooper delivered a similar message.

GOV.

ROY COOPER (D-NC): Kamala Harris is## the person.

She's excited to# win th.. LAURA BARRON-LOPEZ: Meanwhile, Michigan# Governor Gretchen Whitmer gave her endorsement,## but said she would not accept the# vice presidency if offered it.

QUESTION: If they offer it, you will not take it?

GOV.

GRETCHEN WHITMER (D-MI):# I am not leaving Michigan.

LAURA BARRON-LOPEZ: Pennsylvania# governor Josh Shapiro, California## Governor Gavin Newsom and Illinois Governor# J.B. Pritzker also said they support Harris.

Though holding back an endorsement, West# Virginia Senator Joe Manchin confirmed## today that he will not challenge the# vice president for the nomination.

QUESTION: So, you are not interested in# running for office, true, for the presidency?

SEN. JOE MANCHIN (I-WV): I'm not# running.

I'm not running for office.

LAURA BARRON-LOPEZ: On the right,# a different story.

House Speaker## Mike Johnson rebuked Biden's decision to drop out.

He wrote in a statement that it invalidated# the votes of more than 14 million Americans## and joined other Republicans in calling# for Biden to resign from the presidency.

Former President Trump lambasted the move on# TRUTH Social, falsely saying of the Democrats:## "They stole the race from Biden after he won it in## the primaries.

These people are# the real threat to democracy."

And team Trump is already# attacking their new opponent,## including Trump's running mate, J.D.# Vance, at a rally in his hometown today.

SEN. J.D.

VANCE (R-OH), Vice Presidential# Candidate: If you want to lead this country,## you should feel grateful for it.

You# should feel a sense of gratitude.## And I never hear that gratitude come# through when I listen to Kamala Harris.

(CHEERING) (APPLAUSE) for the second full day of# her campaign for president.

Despite Trump's fast attacks on Harris, Democrats# are energized and are trying to turn the tables on## the Republican narrative, pointing out that Trump# is now the oldest presidential nominee in history.

AMNA NAWAZ: Laura, you have been reporting for# weeks on the growing calls for President Biden to## step aside, but tell us how he ultimately arrived# at the decision to do so just this past weekend.

LAURA BARRON-LOPEZ: Sources familiar with# the decision-making, Amna, told me that,## up until Saturday, President Biden was still# holding firm, still wanting to stay in this race.

And President Biden was alone for much of his# COVID isolation, which started last Wednesday,## until his two closest longtime advisers, Steve# Ricchetti and Mike Donilon, arrived and huddled## with him on Saturday.

They gave him the lay# of the land essentially for his campaign,## talking to him about him losing support in# Congress, about donors shutting off money.

They ran through polling with him, sources# told me.

And it wasn't until Sunday,## when President Biden decided he was ultimately# going to bow out of this race.

And all of his## other senior advisers, including Jen# O'Malley Dillon, the campaign chair,## as well as Jeff Zients, who is the chief of# staff to the president at the White House,## were not aware of this decision until about# 1:45 p.m. On Sunday, literally one minute,## Amna, before the president posted# on X his announcement about it.

So they were finding out in real time.

I also# spoke to Senator Chris Coons of Delaware,## a longtime ally of Biden, who said that# the president really was weighing staying## in this fight.

He was deeply torn,# didn't want to get out of this race,## but ultimately felt it was the# right decision for the country.

And Senator Coons said that he felt as# though months of relentless focus on the## debate is ultimately what hurt President Biden's# polling numbers, more than the debate itself.

AMNA NAWAZ: Remarkable few# weeks in political history.

So what happens next?

Walk us through what a## potential nominating process for# the Democrats could look like.

LAURA BARRON-LOPEZ: So the Democratic# National Committee Rules Committee is## going to be meeting Wednesday of this week# to establish a framework for how the process## is going to work for nominating, be# it Kamala Harris or another nominee.

I spoke to members of the DNC Rules# Committee, who said that one of the## biggest questions that they're going to be# addressing this week is whether or not they're## going to still hold a virtual roll call vote# ahead of the physical convention in Chicago.

That would be some time between August# 1 through 5.

The actual convention is in## mid-August.

And so they're trying to figure# out if they're still going to hold it early,## because they want to be on the# strongest footing possible to## basically fight off potential Republican# litigation regarding ballot access.

And so it's highly likely that they will still# move forward with that virtual roll call vote,## based on the people that I was talking# to on the Rules Committee.

And a lot## of them do expect that Kamala# Harris will be their nominee.

AMNA NAWAZ: And you mentioned# some of the key folks already## that we have seen come out to back# Harris as the Democratic nominee.

Is## that what we're seeing across the# rest of the Democratic Party too?

LAURA BARRON-LOPEZ: We are.

She is shoring up support very quickly with.. President Harris went to Wilmington, Delaware,# to what was Biden H.Q., which is now Harris H.Q.,## and President Biden phoned in while she was# there, saying that he hoped that his staff## would give as much of their heart and soul# to Vice President Harris as they did to him.

But, notably, one of the big endorsers# for Vice President Harris is Nancy Pelosi,## the former speaker, who had expressed# to some members that she wanted a more## competitive process.

But Harris has secured# endorsements from not just Nancy Pelosi,## but all of her would-be challengers,# including Governors Whitmer, Shapiro,## Newsom, and Pritzker, all 50 state# Democratic Party chairs endorsed Harris.

Notably, though, House Minority Leader# Hakeem Jeffries and Senate Majority Leader## Chuck Schumer have not endorsed her yet.# They're expected to meet with her soon,## sometime this week.

Hakeem Jeffries said# that he thinks she's off to a great start,## but when asked by reporters# today did not endorse her.

AMNA NAWAZ: So if she were# to secure the nomination,## what are you hearing about who she# might pick as a potential running mate?

LAURA BARRON-LOPEZ: So those considered to be# on her short list include Governor Roy Cooper of## North Carolina, Governor Andy Beshear of Kentucky,# and then also Senator Mark Kelly of Arizona,## a notable swing state there, as well as# Governor Josh Shapiro of Pennsylvania,## another big battleground state there, and then,# finally, Governor Jared Polis of Colorado.

All of those men, I'm told, are being# considered potentially for her to be## her vice president.

And multiple sources have# also told me that they expect Vice President## Harris to pick her own vice presidential# candidate as early as this week, Amna.

So Democrats are moving on a really fast# timeline here because of the fact that they## may very well hold that roll call vote for their# nominee ahead of their convention in mid-August.

AMNA NAWAZ: Laura Barron-Lopez with a# whirlwind 24 hours in politics and reporting.

Laura, thank you.

LAURA BARRON-LOPEZ: Thank you.