Washington (CNN) Elizabeth Warren and Hillary Clinton met Friday, a day after the Massachusetts senator endorsed the presumptive Democratic presidential nominee and called on Democrats to unite behind her.

As expected, the two huddled Friday morning at Clinton's Washington, D.C., home.

On Thursday, Warren finally endorsed Clinton after being one of the lone hold outs in the Senate.

"I'm ready to get in this fight and work my heart out for Hillary Clinton to become the next president of the United States and to make sure that Donald Trump never gets any place close to the White House," Warren told MSNBC's Rachel Maddow.

After conceding the presidency to Trump in a phone call earlier, Clinton addresses supporters and campaign workers in New York on Wednesday, November 9. Her defeat marked a stunning end to a campaign that appeared poised to make her the first woman elected US president.

Clinton addresses a campaign rally in Cleveland on November 6, two days before Election Day. She went on to lose Ohio -- and the election -- to her Republican opponent, Donald Trump.

Clinton addresses a campaign rally in Cleveland on November 6, two days before Election Day. She went on to lose Ohio -- and the election -- to her Republican opponent, Donald Trump.

Clinton arrives at a 9/11 commemoration ceremony in New York on September 11. Clinton, who was diagnosed with pneumonia two days before, left early after feeling ill. A video appeared to show her stumble as Secret Service agents helped her into a van.

Obama hugs Clinton after he gave a speech at the Democratic National Convention in Philadelphia. The president said Clinton was ready to be commander in chief. "For four years, I had a front-row seat to her intelligence, her judgment and her discipline," he said, referring to her stint as his secretary of state.

Obama hugs Clinton after he gave a speech at the Democratic National Convention in Philadelphia. The president said Clinton was ready to be commander in chief. "For four years, I had a front-row seat to her intelligence, her judgment and her discipline," he said, referring to her stint as his secretary of state.

After Clinton became the Democratic Party's presumptive nominee, this photo was posted to her official Twitter account. "To every little girl who dreams big: Yes, you can be anything you want -- even president," Clinton said. "Tonight is for you."

After Clinton became the Democratic Party's presumptive nominee, this photo was posted to her official Twitter account. "To every little girl who dreams big: Yes, you can be anything you want -- even president," Clinton said. "Tonight is for you."

Clinton walks on her stage with her family after winning the New York primary in April.

Clinton walks on her stage with her family after winning the New York primary in April.

Clinton is reflected in a teleprompter during a campaign rally in Alexandria, Virginia, in October 2015.

Clinton is reflected in a teleprompter during a campaign rally in Alexandria, Virginia, in October 2015.

U.S. Sen. Bernie Sanders shares a lighthearted moment with Clinton during a Democratic presidential debate in October 2015. It came after Sanders gave his take on the Clinton email scandal. "The American people are sick and tired of hearing about the damn emails," Sanders said. "Enough of the emails. Let's talk about the real issues facing the United States of America."

U.S. Sen. Bernie Sanders shares a lighthearted moment with Clinton during a Democratic presidential debate in October 2015. It came after Sanders gave his take on the Clinton email scandal. "The American people are sick and tired of hearing about the damn emails," Sanders said. "Enough of the emails. Let's talk about the real issues facing the United States of America."

Clinton testifies about the Benghazi attack during a House committee meeting in October 2015. "I would imagine I have thought more about what happened than all of you put together," she said during the 11-hour hearing. "I have lost more sleep than all of you put together. I have been wracking my brain about what more could have been done or should have been done." Months earlier, Clinton had acknowledged a "systemic breakdown" as cited by an Accountability Review Board, and she said that her department was taking additional steps to increase security at U.S. diplomatic facilities.

Clinton testifies about the Benghazi attack during a House committee meeting in October 2015. "I would imagine I have thought more about what happened than all of you put together," she said during the 11-hour hearing. "I have lost more sleep than all of you put together. I have been wracking my brain about what more could have been done or should have been done." Months earlier, Clinton had acknowledged a "systemic breakdown" as cited by an Accountability Review Board, and she said that her department was taking additional steps to increase security at U.S. diplomatic facilities.

Clinton, now running for President again, performs with Jimmy Fallon during a "Tonight Show" skit in September 2015.

Clinton, now running for President again, performs with Jimmy Fallon during a "Tonight Show" skit in September 2015.

Clinton ducks after a woman threw a shoe at her while she was delivering remarks at a recycling trade conference in Las Vegas in 2014.

Clinton ducks after a woman threw a shoe at her while she was delivering remarks at a recycling trade conference in Las Vegas in 2014.

Obama and Clinton bow during the transfer-of-remains ceremony marking the return of four Americans, including U.S. Ambassador Christopher Stevens, who were killed in Benghazi, Libya, in September 2012.

Obama and Clinton bow during the transfer-of-remains ceremony marking the return of four Americans, including U.S. Ambassador Christopher Stevens, who were killed in Benghazi, Libya, in September 2012.

Clinton arrives for a group photo before a forum with the Gulf Cooperation Council in March 2012. The forum was held in Riyadh, Saudi Arabia.

Clinton arrives for a group photo before a forum with the Gulf Cooperation Council in March 2012. The forum was held in Riyadh, Saudi Arabia.

Clinton checks her Blackberry inside a military plane after leaving Malta in October 2011. In 2015, The New York Times reported that Clinton exclusively used a personal email account during her time as secretary of state. The account, fed through its own server, raises security and preservation concerns. Clinton later said she used a private domain out of "convenience," but admits in retrospect "it would have been better" to use multiple emails.

Clinton checks her Blackberry inside a military plane after leaving Malta in October 2011. In 2015, The New York Times reported that Clinton exclusively used a personal email account during her time as secretary of state. The account, fed through its own server, raises security and preservation concerns. Clinton later said she used a private domain out of "convenience," but admits in retrospect "it would have been better" to use multiple emails.

In this photo provided by the White House, Obama, Clinton, Biden and other members of the national security team receive an update on the mission against Osama bin Laden in May 2011.

In this photo provided by the White House, Obama, Clinton, Biden and other members of the national security team receive an update on the mission against Osama bin Laden in May 2011.

The Clintons pose on the day of Chelsea's wedding to Marc Mezvinsky in July 2010.

The Clintons pose on the day of Chelsea's wedding to Marc Mezvinsky in July 2010.

Clinton, as secretary of state, greets Russian Prime Minister Vladimir Putin during a meeting just outside Moscow in March 2010.

Clinton, as secretary of state, greets Russian Prime Minister Vladimir Putin during a meeting just outside Moscow in March 2010.

Obama is flanked by Clinton and Vice President-elect Joe Biden at a news conference in Chicago in December 2008. He had designated Clinton to be his secretary of state.

Obama is flanked by Clinton and Vice President-elect Joe Biden at a news conference in Chicago in December 2008. He had designated Clinton to be his secretary of state.

Obama and Clinton talk on the plane on their way to a rally in Unity, New Hampshire, in June 2008. She had recently ended her presidential campaign and endorsed Obama.

Obama and Clinton talk on the plane on their way to a rally in Unity, New Hampshire, in June 2008. She had recently ended her presidential campaign and endorsed Obama.

Clinton and another presidential hopeful, U.S. Sen. Barack Obama, applaud at the start of a Democratic debate in 2007.

Clinton and another presidential hopeful, U.S. Sen. Barack Obama, applaud at the start of a Democratic debate in 2007.

Clinton holds up her book "Living History" before a signing in Auburn Hills, Michigan, in 2003.

Clinton holds up her book "Living History" before a signing in Auburn Hills, Michigan, in 2003.

Sen. Clinton comforts Maren Sarkarat, a woman who lost her husband in the September 11 terrorist attacks, during a ground-zero memorial in October 2001.

Sen. Clinton comforts Maren Sarkarat, a woman who lost her husband in the September 11 terrorist attacks, during a ground-zero memorial in October 2001.

Clinton makes her first appearance on the Senate Environment and Natural Resources Committee.

Clinton makes her first appearance on the Senate Environment and Natural Resources Committee.

Clinton announces in February 2000 that she will seek the U.S. Senate seat in New York. She was elected later that year.

Clinton announces in February 2000 that she will seek the U.S. Senate seat in New York. She was elected later that year.

President Clinton makes a statement at the White House in December 1998, thanking members of Congress who voted against his impeachment. The Senate trial ended with an acquittal in February 1999.

President Clinton makes a statement at the White House in December 1998, thanking members of Congress who voted against his impeachment. The Senate trial ended with an acquittal in February 1999.

The first family walks with their dog, Buddy, as they leave the White House for a vacation in August 1998.

The first family walks with their dog, Buddy, as they leave the White House for a vacation in August 1998.

Clinton looks on as her husband discusses the Monica Lewinsky scandal in the Roosevelt Room of the White House on January 26, 1998. Clinton declared, "I did not have sexual relations with that woman." In August of that year, Clinton testified before a grand jury and admitted to having "inappropriate intimate contact" with Lewinsky, but he said it did not constitute sexual relations because they had not had intercourse. He was impeached in December on charges of perjury and obstruction of justice.

Clinton looks on as her husband discusses the Monica Lewinsky scandal in the Roosevelt Room of the White House on January 26, 1998. Clinton declared, "I did not have sexual relations with that woman." In August of that year, Clinton testified before a grand jury and admitted to having "inappropriate intimate contact" with Lewinsky, but he said it did not constitute sexual relations because they had not had intercourse. He was impeached in December on charges of perjury and obstruction of justice.

The Clintons dance on a beach in the U.S. Virgin Islands in January 1998. Later that month, Bill Clinton was accused of having a sexual relationship with former White House intern Monica Lewinsky.

The Clintons dance on a beach in the U.S. Virgin Islands in January 1998. Later that month, Bill Clinton was accused of having a sexual relationship with former White House intern Monica Lewinsky.

The first lady holds up a Grammy Award, which she won for her audiobook "It Takes a Village" in 1997.

The first lady holds up a Grammy Award, which she won for her audiobook "It Takes a Village" in 1997.

The Clintons hug as Bill is sworn in for a second term as President.

The Clintons hug as Bill is sworn in for a second term as President.

Clinton waves to the media in January 1996 as she arrives for an appearance before a grand jury in Washington. The first lady was subpoenaed to testify as a witness in the investigation of the Whitewater land deal in Arkansas. The Clintons' business investment was investigated, but ultimately they were cleared of any wrongdoing.

Clinton waves to the media in January 1996 as she arrives for an appearance before a grand jury in Washington. The first lady was subpoenaed to testify as a witness in the investigation of the Whitewater land deal in Arkansas. The Clintons' business investment was investigated, but ultimately they were cleared of any wrongdoing.

Clinton unveils the renovated Blue Room of the White House in 1995.

Clinton unveils the renovated Blue Room of the White House in 1995.

The Clintons share a laugh on Capitol Hill in 1993.

The Clintons share a laugh on Capitol Hill in 1993.

Clinton accompanies her husband as he takes the oath of office in January 1993.

Clinton accompanies her husband as he takes the oath of office in January 1993.

During the 1992 presidential campaign, Clinton jokes with her husband's running mate, Al Gore, and Gore's wife, Tipper, aboard a campaign bus.

During the 1992 presidential campaign, Clinton jokes with her husband's running mate, Al Gore, and Gore's wife, Tipper, aboard a campaign bus.

In June 1992, Clinton uses a sewing machine designed to eliminate back and wrist strain. She had just given a speech at a convention of the International Ladies' Garment Workers Union.

In June 1992, Clinton uses a sewing machine designed to eliminate back and wrist strain. She had just given a speech at a convention of the International Ladies' Garment Workers Union.

Bill Clinton comforts his wife on the set of "60 Minutes" after a stage light broke loose from the ceiling and knocked her down in January 1992.

Bill Clinton comforts his wife on the set of "60 Minutes" after a stage light broke loose from the ceiling and knocked her down in January 1992.

The Clintons celebrate Bill's inauguration in Little Rock, Arkansas, in 1991. He was governor from 1983 to 1992, when he was elected President.

The Clintons celebrate Bill's inauguration in Little Rock, Arkansas, in 1991. He was governor from 1983 to 1992, when he was elected President.

Arkansas' first lady, now using the name Hillary Rodham Clinton, wears her inaugural ball gown in 1985.

Arkansas' first lady, now using the name Hillary Rodham Clinton, wears her inaugural ball gown in 1985.

In 1975, Rodham married Bill Clinton, whom she met at Yale Law School. He became the governor of Arkansas in 1978. In 1980, the couple had a daughter, Chelsea.

In 1975, Rodham married Bill Clinton, whom she met at Yale Law School. He became the governor of Arkansas in 1978. In 1980, the couple had a daughter, Chelsea.

Rodham was a lawyer on the House Judiciary Committee, whose work led to impeachment charges against President Richard Nixon in 1974.

Rodham was a lawyer on the House Judiciary Committee, whose work led to impeachment charges against President Richard Nixon in 1974.

Before marrying Bill Clinton, she was Hillary Rodham. Here she attends Wellesley College in Massachusetts. Her commencement speech at Wellesley's graduation ceremony in 1969 attracted national attention. After graduating, she attended Yale Law School.

Before marrying Bill Clinton, she was Hillary Rodham. Here she attends Wellesley College in Massachusetts. Her commencement speech at Wellesley's graduation ceremony in 1969 attracted national attention. After graduating, she attended Yale Law School.

Hillary Clinton accepts the Democratic Party's nomination for president at the Democratic National Convention in Philadelphia on July 28, 2016. The former first lady, U.S. senator and secretary of state was the first woman to lead the presidential ticket of a major political party.

Hillary Clinton accepts the Democratic Party's nomination for president at the Democratic National Convention in Philadelphia on July 28, 2016. The former first lady, U.S. senator and secretary of state was the first woman to lead the presidential ticket of a major political party.

Warren's endorsement comes after both President Barack Obama and Vice President Joe Biden backed the former secretary of state on Thursday.

"I don't think there's ever been someone so qualified to hold this office," Obama said.

Warren, a liberal stalwart known for championing issues related to economic inequality, has been one of the few Democratic senators to withhold a formal presidential endorsement.

"I thought that the primary was really important and it was an opportunity for Democrats to get out there and show this is what it means to be a Democrat," Warren said when asked why she withheld her endorsement for Clinton or primary rival Bernie Sanders.

"What Bernie Sanders did was powerfully important. He ran a campaign from the heart.... He brought millions of people into the Democratic Party and for me, this is what it's all about," the Massachusetts senator added.

Clinton reacted to Warren's endorsement on Twitter, writing: "Proud to have the support of @SenWarren -- a woman who is Trump's exact opposite: honest, decent, and deeply concerned for working families. -H."

Proud to have the support of @SenWarren—a woman who is Trump's exact opposite: honest, decent, and deeply concerned for working families. -H — Hillary Clinton (@HillaryClinton) June 10, 2016

Warren had already delivered a blistering critique of Donald Trump Thursday evening during a speech in Washington, continuing her recent role as antagonist to the presumptive Republican presidential nominee.

Photos: The women who have run for president Photos: The women who have run for president American feminist reformer Victoria Woodhull was the first woman to run for U.S. president from a nationally recognized ticket as the candidate of the Equal Rights Party in 1872. Woodhull was also one of the first female stockbrokers on Wall Street. Hide Caption 1 of 19 Photos: The women who have run for president Belva Lockwood was the first woman to practice law in front of the U.S. Supreme Court. She ran for president in 1884 and 1888 on the Equal Rights Party ticket. Hide Caption 2 of 19 Photos: The women who have run for president Gracie Allen made a farcical run for president in 1940. Campaigning under the Surprise Party platform, Allen -- with husband George Burns -- went on a whistle-stop tour of the country. Hide Caption 3 of 19 Photos: The women who have run for president Sen. Margaret Chase Smith was the first woman to serve in the House of Representatives and Senate. She was also the first woman to be placed in nomination for the presidency at a major party's convention (the Republican National Convention in 1964). Hide Caption 4 of 19 Photos: The women who have run for president Charlene Mitchell was the Communist Party USA nominee for president in 1968 and also challenged Daniel Patrick Moynihan, D-New York, for the Senate in 1988. Hide Caption 5 of 19 Photos: The women who have run for president U.S. Rep. Shirley Chisholm announces her entry for Democratic nomination for the presidency in 1972 in Brooklyn, New York. Chisholm was the first African-American female candidate from a major party. Hide Caption 6 of 19 Photos: The women who have run for president Linda Jenness was the Socialist Workers Party candidate for president in 1972. Hide Caption 7 of 19 Photos: The women who have run for president Margaret Wright was the Peace and Freedom Party presidential candidate in 1976. Her running mate was Dr. Benjamin Spock. Hide Caption 8 of 19 Photos: The women who have run for president Maureen Smith was the Peace and Freedom Party presidential candidate in 1980. Hide Caption 9 of 19 Photos: The women who have run for president Feminist activist and writer Sonia Johnson ran in 1984 as the presidential candidate of the U.S. Citizens Party, Pennsylvania's Consumer Party and California's Peace and Freedom Party. Hide Caption 10 of 19 Photos: The women who have run for president Lenora Fulani ran for president in 1988 and 1992 as a candidate of the New Alliance Party. Here, she holds a news conference at Atlanta City Hall in July 1988. Hide Caption 11 of 19 Photos: The women who have run for president Elvena Lloyd-Dufﬁe ran as a Democratic candidate against incumbent Bill Clinton in 1996. Hide Caption 12 of 19 Photos: The women who have run for president Elizabeth Dole unsuccessfully sought the GOP nomination for president in 2000. She is a former U.S. senator from North Carolina and served as U.S. secretary of transportation under Ronald Reagan and secretary of labor under George H.W. Bush. She is the wife of former Sen. Bob Dole, the 1996 Republican nominee for president. Hide Caption 13 of 19 Photos: The women who have run for president Former Sen. Carol Moseley-Braun of Illinois sought the 2004 Democratic presidential nomination. Hide Caption 14 of 19 Photos: The women who have run for president Hillary Clinton, the presumptive Democratic nominee for 2016, noted in 2008 that the glass ceiling had "18 million cracks in it" -- a reference to the number of votes she received in the 2008 Democratic primary before conceding the race to Barack Obama. Hide Caption 15 of 19 Photos: The women who have run for president Cynthia McKinney was the Green Party presidential candidate in 2008. McKinney was a six-term Democratic congresswoman from Georgia before running for president. Hide Caption 16 of 19 Photos: The women who have run for president Roseanne Barr announces she is a candidate for president on "The Tonight Show with Jay Leno" in 2011. She won the 2012 nomination of the Peace and Freedom Party. Hide Caption 17 of 19 Photos: The women who have run for president Dr. Jill Stein is the 2016 Green Party presidential candidate. She was also the party's presidential candidate in 2012. Hide Caption 18 of 19 Photos: The women who have run for president Former Hewlett-Packard CEO Carly Fiorina marches with her family in the Labor Day parade in 2015 in Milford, New Hampshire. Fiorina unsuccessfully sought the GOP presidential nomination in 2016 and then briefly joined Sen. Ted Cruz as his running mate before he suspended his campaign. Hide Caption 19 of 19

A Sanders aide told CNN's Jeff Zeleny Thursday night that Sanders and Warren spoke by phone earlier in the evening after attempts to reach him in advance of her endorsement.

A source said the decision was made for Warren to endorse Clinton Thursday, on the heels of Obama's endorsement, "To make it more forceful for the overall goal."

The Republican National Committee wasted no time blasting Warren after news of the endorsement surfaced.

"By endorsing Hillary Clinton, Elizabeth Warren has shown herself to be a sellout," RNC spokeswoman Lindsay Walters said in a statement. "Whether it's the Wall Street speech transcripts she refuses to release, her ties to the fossil fuel industry, or coziness with big banks, Hillary Clinton represents everything Elizabeth Warren supposedly stands against."

In the television interview Thursday night, Warren batted down speculation of Clinton tapping her as the vice presidential nominee. Warren responded with a flat "no" when asked if she has had conversations with the Clinton campaign.

"I know there's been a lot of speculation about this," Warren said, adding "the truth is I love the work I do. I can't tell you who grateful I am to the people of Massachusetts who sent me here to wade into these fights."

Warren was asked about comments by former Pennsylvania Gov. Ed Rendell -- a Clinton supporter -- that she is "not ready to be commander-in-chief."

Queried on whether she thinks she is ready, Warren responded, "Yes, I do."