Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) signed a pledge on Tuesday agreeing to formally run for president in 2020 as a Democrat, a spokesperson for the longtime Independent lawmaker's campaign said.

The move came in response to a rule passed by the Democratic National Committee (DNC) last year that anyone seeking the party’s 2020 presidential nomination must do so as a Democrat.

Sanders's supporters viewed the rule change as directly focused on him after the self-described democratic socialist sought the Democratic presidential nomination in 2016 without formally declaring himself a member of the party.

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The Independent Vermont senator caucuses with Democrats in the Senate but has long refused to consider himself a member of the Democratic Party.

Sanders filed to run for president in February as a Democrat and a campaign adviser said last month he planned to sign the DNC. pledge.

Still, he also filed on Monday to run for reelection to his Senate seat in 2024 as an Independent.

The topic of party affiliation has long rankled some in the Democratic Party, who say that Sanders has tried to reap the benefit of the party establishment while refusing to support the party as a whole.

At the same time, some of Sanders’s supporters have accused the DNC of trying to strong-arm the Vermont senator into joining the party.

During his 2016 White House bid, Sanders briefly registered as a Democrat to run in the New Hampshire primary, although he later un-enrolled in the party.