Ellison was an early supporter of Vermont Sen. Bernie Sanders in the Democratic presidential primary. Sanders launched a petition last week in support of the congressman, touting him as "a strong believer in grassroots politics, and someone who would be enormously effective in leading the Democratic Party against President Donald Trump."

Former DNC chairwoman Debbie Wasserman Schultz resigned from the post in July, just before the party's national convention, following the release of hacked emails suggesting a preference among the DNC for former Secretary of State Hillary Clinton over Sanders.

Baldwin, in her endorsement of Ellison, said she hears "the voices of Americans who are angry because they feel Washington is broken and it isn't working for them."

"I also share deeply the concerns of our friends and neighbors who are afraid because they don't believe the Republican establishment in Washington is committed to the idea that we are stronger together, that America is great because we are a diverse and inclusive nation," she said.