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.) plans to sign a pledge saying he will run as a Democrat in his bid for the presidency in 2020 and to govern as a Democrat if elected, campaign adviser Jeff Weaver told CNN.

The revelation comes one day after Sanders announced his plans to run for the presidency again in 2020 after an unsuccessful but competitive bid in 2016.

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Sanders, an independent from Vermont, has drawn the ire of some Democrats for not fully embracing the party in the past, CNN noted.

Under new Democratic National Committee rules, Democratic candidates seeking the party's nomination will be asked to pledge in writing that they will run and govern as a member of the Democratic Party.

A DNC official told CNN that, in the coming days, the DNC will present the candidates that have already announced their candidacy or formed an exploratory committee with a form that they will be asked to return, affirming their intention to run as Democrats.

"As any additional candidates enter the race, they will be provided with the same information and will be required to return the form in the same time frame," the official added.