Warren associates and the camp of former vice president Joe Biden also had talks about a potential endorsement if she drops out, according to two people familiar with the conversations.
The whirlwind of activity reflects the rapid changes in a Democratic primary that is still very much in transition. As late as Tuesday, many Warren allies believed she would stay in the race until the Democratic convention, despite her poor showing to date in the primaries, in hopes of retaining her clout and influencing the eventual nominee.
But after Warren's bleak performance in the Super Tuesday primaries, her associates, as well as those of Sanders and Biden, say she is now looking for the best way to step aside. There is no certainty she will endorse Sanders or anyone else, but the talks reflect the growing pressure on the senator from Massachusetts to withdraw.
Warren campaign manager Roger Lau suggested Wednesday she was considering that. "Last night, we fell well short of viability goals and projections, and we are disappointed in the results," he wrote to campaign staffers in a note obtained by The Washington Post. "We are going to announce shortly that Elizabeth is talking to the team to assess the path forward."
Warren and Sanders spoke by phone Wednesday, Sanders told reporters in Vermont. "She has not made any decisions as of this point," he said. "It is important for all of us, certainly me, who has known Elizabeth Warren for many, many years, to respect the time and the space she needs to make a decision."
"She has run a strong campaign," Sanders said. "She will make her own decision in her own time."
Liberal groups that endorsed Sanders are now planning a conference call for Thursday, in part to discuss the impact of Warren's candidacy on the race and the potential effect of a withdrawal.
Winning the backing of Warren, who began the race as a leader of the party's liberal wing but later positioned herself as a uniter, would be a coup for either Sanders or Biden. For Sanders, it could help unify the liberal faction and signal that he is very much still in the race; for Biden, it would extend the recent rush of party leaders who have rallied around him.
Warren's status is a major wild card in a primary that appears to be settling into a protracted battle between Biden and Sanders. Other candidates with no clear path to the nomination have dropped out, but her aides say privately they had hoped Warren would stay in until the next Democratic debate, on March 15.
Warren may be the only female candidate to qualify for that debate, and her departure would leave Democrats essentially deciding between two white men in their late 70s — after the party's last two presidential nominees were a black man and a white woman.
Her debate skills have been a high point of her campaign, showcasing her mastery of policy and her intellectual deftness — particularly in the Las Vegas debate, when she verbally disassembled former New York mayor Mike Bloomberg, arguably ending his campaign.
And despite a string of disappointing finishes in the early primary states, Warren continued to draw thousands of people to her rallies, including recent events in Seattle, Denver, Houston and Detroit.
Money, too, has continued to flow. Her campaign raised $29 million in February, compared with Biden's $18 million haul for that month. Warren also has the support of a super PAC that's been airing $14 million worth of TV ads for her.
She finished third in her home state of Massachusetts and fourth in Oklahoma, where she grew up. She reached the 15 percent statewide threshold, which is necessary to win significant numbers of delegates, in only five of the 14 states that voted Tuesday.
On Tuesday, when Warren voted in her home precinct — at an elementary school in Cambridge — young students dropped red and white rose petals from their second-floor window as she walked by. They pressed against windows to catch a glimpse of her, and she waved at them after voting.
But Warren has also been facing mounting pressure from liberal activists and Sanders supporters to depart the race. They argue that she is hurting the senator from Vermont by dividing the party’s liberal faction, while Democratic centrists have coalesced behind Biden. Sanders also fell below expectations Tuesday, as Biden rolled up big margins.
Rep. Ilhan Omar (D-Minn.), a Sanders backer and leading voice on the left, said via Twitter: “Imagine if the progressives consolidated last night like the moderates consolidated, who would have won?”
Omar added: “That’s what we should be analyzing. I feel confident a united progressive movement would have allowed for us to #BuildTogether and win MN and other states we narrowly lost.” Sanders lost Minnesota by nearly nine percentage points, results show.
Other left-leaning groups have been pressuring her for weeks to depart.
“She should drop out of the race and endorse Bernie Sanders,” said Matt Bruenig, founder of the People’s Policy Project, a liberal think tank, whose group has been pushing for her exit since her fourth-place finish in New Hampshire.
“The questions is how to get her to prioritize that this [a progressive agenda] is a more important thing than whatever it is she hopes to achieve by staying in,” Bruenig said.
It is not clear that Warren would immediately — or ever — back Sanders. She stayed on the sidelines during the 2016 Democratic primary between Sanders and Hillary Clinton, eventually throwing her support to Clinton and hoping to be selected as her running mate.
Warren also met with Biden in 2015 as he was considering a presidential bid of his own. At the time Biden floated the idea that they could join forces on the same ticket, but soon he decided not to challenge Clinton.
As it became clearer Wednesday that Warren was seriously considering leaving the race, liberal groups became increasingly magnanimous.
"The decision of whether or not to drop out is her decision and her decision alone," said Charles Chamberlain, chair of Democracy for America. "We don't think that anybody in the progressive movement should be calling on a woman — especially the last woman — to drop out." (Rep. Tulsi Gabbard of Hawaii remains in the race but has not met the criteria to participate in any recent debates.)
Chamberlain said he would urge other groups backing Sanders to take a similar approach Thursday during the organization's conference call, and respect a decision either to remain on the debate stage or to endorse Sanders.
He added, "The bottom line is that progressives trust Elizabeth Warren, and we're confident that she's going to make the right choice here."
Sullivan reported from Burlington, Vt. Dan Balz contributed to this report.