Some of Sen. Bernie Sanders Bernie SandersSenate Republicans signal openness to working with Biden Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Schumer, Sanders call for Senate panel to address election security MORE' (I-Vt.) top aides and supporters have urged the 2020 Democratic presidential candidate to drop out of the primary race, sources familiar with the situation told The Washington Post.

Sanders' campaign manager Faiz Shakir and Rep. Pramila Jayapal Pramila JayapalProgressive Caucus co-chair: Whistleblower complaint raises questions about 'entire detention system' Buttigieg, former officials added to Biden's transition team A Biden-Harris presidency would largely end oil and gas production MORE (D-Wash.), one of the senator's top surrogates, were both part of the group that has pressed for him to suspend his campaign, according to the sources.

Other Sanders aides and allies such as national campaign co-chair Nina Turner have reportedly encouraged the 78-year-old to stay in the race.

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“Millions of people are counting on him to be on the ballot so they can vote for that alternative vision that they support,” Larry Cohen, a longtime supporter who chairs a nonprofit associated with Sanders, told the Post. “If he was not on the ballot, they will feel abandoned.”

The Democratic presidential nomination has become increasingly difficult for Sanders to win since former Vice President Joe Biden Joe BidenThe Memo: Warning signs flash for Trump on debates Senate Republicans signal openness to working with Biden National postal mail handlers union endorses Biden MORE routed him on Super Tuesday, winning most of the contests that day.

Biden then proceeded to win majority of the next two slates of primaries, giving him a large lead in delegates. A candidate needs 1,991 delegates to secure the nomination and Biden has 1,217 while Sanders has 914.

The next primary is Wisconsin on Tuesday, which polls predict Biden will win handedly.