Elizabeth Warren still hasn't endorsed Joe Biden.

Her support is inevitable since the once historically crowded Democratic primary field has come down to one man over the course of the past year. But the Massachusetts senator and former 2020 presidential candidate has declined to back the two-term vice president after dropping out of the White House race following Super Tuesday.

"Well, let's take a deep breath and spend a little time on that," Warren told reporters in March. "We don’t have to decide that this minute."

Yet her silence is now conspicuous given Biden's chief Democratic rival, Vermont Sen. Bernie Sanders, and his ex-boss, former President Barack Obama, both endorsed the presumptive nominee this week. Obama, in particular, withstood sustained pressure to weigh in on the contest on behalf of his eight-year understudy, remaining neutral until the party had an apparent standard-bearer.

However, Jonathan Cohn, chairman of the Issues Committee of Progressive Massachusetts, wasn't surprised by Warren's endorsement approach. Warren waited until June 2016 to support Hillary Clinton after the former first lady, New York senator, and secretary of state trounced Sanders in California, cementing her delegate lead so she could earn the party's nod that cycle.

"My take: Given that Elizabeth Warren stayed out in 2016 out of a desire to use leverage to push Hillary Clinton to the left on policy and personnel, I would assume that she has made policy and personnel demands of Biden that would have to be met before an endorsement rollout," Cohn told the Washington Examiner.

Years before the 2016 election, Warren launched a quiet campaign to exert influence on Clinton. As part of that effort, she suggested economic advisers who were critical of Obama's 2008 financial crisis response and blacklisted potential Clinton administration nominees with Wall Street ties who were antithetical to Warren's careerlong work as a banking watchdog.

This round, she ended up seeking the presidency herself.

In the meantime, Sanders, who bowed out of contention last week, announced the formation of joint Biden-Sanders policy task forces along with his endorsement.

Before Sanders unveiled his support, Biden embraced elements of his education platform, including making public colleges and universities free for students from low-income and middle-class families and forgiving tuition debt for the same type of students who attended public colleges and universities or private historically black colleges and underfunded minority-serving institutions.

Though falling short of Sanders's vision for a single-payer healthcare system such as his signature Medicare for All bill, Biden also vowed to lower Medicare's eligibility age requirement from 65 to 60. Biden revealed the policies after Sanders said he'd continue racking up delegates ahead of the party's convention in Milwaukee, Wisconsin, in August despite suspending his bid.

But Biden's adoption of Warren's bankruptcy reform plan hasn't moved the senator publicly yet.

Biden's decision to take up the proposal was a shock to political observers, as it'd largely undo the law the pair famously fought over in 2005 when he was trying to protect the interests of Delaware's credit card industry as the state's senator. Warren's framework would make it easier for bankrupt individuals and families to seek relief, safeguarding homes and cars from seizure in the process.

For Megan Ottens-Sargent, another Massachusetts Democrat, Warren's endorsement is a matter of timing based on her friendship with ideological ally Sanders, her hope of extracting concessions from Biden, and her senatorial responsibilities amid the novel coronavirus pandemic.

"Some are advocating that Biden pick her as VP. This could swing some Sanders supporters," Ottens-Sargent told the Washington Examiner. "I do not think Warren is jeopardizing a Cabinet position. I think she is cultivating one."

Although intense Democratic dislike of Trump all but guarantees that the party will unite behind Biden, Warren's backing could help close the enthusiasm gap that's plagued his candidacy — even if she doesn't accept a position in his administration, according to the Brookings Institution's Darrell West.

"It is important for Warren to endorse Biden because she is a major progressive leader, and he needs support from the younger voters who pay attention to her," he said. "Biden's endorsement by Barack Obama will encourage Warren and other Democrats to close ranks behind Biden and focus everyone's attention on beating Trump."