WASHINGTON (Reuters) - Bernie Sanders on Tuesday won the endorsement of the Center for Popular Democracy Action, a network of progressive community groups, providing a boost to the U.S. senator’s bid to become the Democratic Party’s nominee for president.

FILE PHOTO: Democratic 2020 U.S. presidential candidate and U.S. Senator Bernie Sanders (I-VT) speaks at a campaign town hall meeting in Portsmouth, New Hampshire, U.S., November 24, 2019. REUTERS/Brian Snyder

The endorsement comes as opinion polls show steady support for Sanders, even as fellow progressive Elizabeth Warren, a U.S. senator from Massachusetts, has slumped in most surveys of voter intentions in the contest to take on Republican President Donald Trump in the November 2020 election.

The Center for Popular Democracy Action, which comprises grassroots groups led by minority and immigrant communities, working families and women, including in hotly contested states, said 75% of its affiliates voted to back Sanders over Warren in the culmination of a months-long deliberation process.

“Bernie Sanders is the powerful movement candidate we need to defeat Donald Trump,” Jennifer Epps-Addison, the group’s co-executive director and president, said in a statement.

“From ending mass incarceration and deportations to the $15 minimum wage and Medicare for All, Sanders is working hand-in-hand with our communities to champion the policies that we need to thrive.”

The Vermont senator, who describes himself as a democratic socialist, has focused his White House run on proposals like his government-run Medicare for All healthcare plan, that he would pay for primarily with raised taxes on corporations and the wealthy.

Sanders, 78, quickly returned to the campaign trail after suffering a heart attack in October, and has gained momentum with the support of high-profile congresswomen including Alexandria Ocasio-Cortez, who had worked for Sanders in his failed 2016 bid to win the Democratic presidential nomination.

A Monmouth University poll released on Tuesday showed 21% of Democrats and Democratic-leaning voters supporting Sanders, up from 15% in September.

Warren was supported by 17% of respondents, compared with 28% in September, when her support peaked.

Both were behind former Vice President Joe Biden, with 26%, but ahead of Pete Buttigieg, the mayor of South Bend, Indiana, who got 8% despite recent polling showing him rising in states that hold their nominating contests early.