With polls suggesting that the Democratic race is getting tighter in the first-caucus state of Iowa and the first-primary state of New Hampshire, Bernie Sanders has won the support of one of the nation’s most prominent progressive networks.

The activist group MoveOn endorsed the Vermont senator after 78.6 percent of its members backed him last week in an online “primary”—which drew 340,665 votes, a greater total than is likely to participate in the February contests in Iowa and New Hampshire.

“This is a massive vote in favor of Bernie Sanders, showing that grassroots progressives across the country are excited and inspired by his message and track record of standing up to big money and corporate interests to reclaim our democracy for the American people,” MoveOn.org Political Action Executive Director Ilya Sheyman said Tuesday. “MoveOn members are feeling the Bern. We will mobilize aggressively to add our collective people power to the growing movement behind the Sanders campaign, starting with a focus on voter turnout in Iowa and New Hampshire.”

MoveOn leaders say they are “poised to mobilize thousands of volunteers, make thousands of phone calls to potential voters, and recruit more small-dollar donors to support Sanders. MoveOn’s first priority will be turning out its 43,000 members in Iowa and 30,000 members in New Hampshire—the first caucus and primary states, where polling shows the candidates running neck-and-neck.”

The front-runner in national polls of Democrats, former secretary of state Hillary Clinton, won 14.6 percent of the votes of MoveOn members, while former Maryland governor Martin O’Malley won just under 1 percent.

But Clinton got some good news on the endorsement front Tuesday, as it was announced that the Brady Campaign to Prevent Gun Violence would back her campaign. Brady Campaign president Dan Gross joined Clinton at an event in Ames, Iowa, where he said, “When it comes to real national leadership on this issue there is so clearly one candidate that rises above all the others—Hillary Clinton.”

The former secretary of state is also backed by the League of Conservation Voters Action Fund, and just last week she won the support of the NARAL Pro-Choice America PAC and the Planned Parenthood Action Fund.

Clinton has a number of major labor-union endorsements, including those of the Service Employees International Union, the American Federation of State County and Municipal Employees, the American Federation of Teachers, and the National Education Association. On Tuesday, the United Food and Commericial Workers union added its support.

Sanders has won endorsements from unions such as National Nurses United, the American Postal Workers Union, and the Communications Workers of America, as well as the environmental group Friends of the Earth Action.

In recent online votes by progressive groups, Sanders has won a number of endorsements. When Democracy for America voted in December, the senator won 88 percent, and the group’s backing. Earlier in the month, when the Working Families Party members voted online, he won 87.4 percent. The WFP also endorsed Sanders, as have Progressive Democrats of America and Democratic Socialists of America.

MoveOn has only made one previous endorsement in a Democratic primary contest, backing then-Senator Barack Obama over Clinton in 2008. The group sets a high threshold for making an endorsement—requiring a two-thirds vote by participating members for a candidate before formal support can be given. In 2004, though former Vermont governor Howard Dean led in voting by MoveOn members, he did not win enough support to clear the bar and secure the endorsement.

This year, members sent a clear signal.

“Bernie’s vote total and percentage are MoveOn records — the best any presidential candidate has performed in our 17-year history,” explained MoveOn executive director Sheyman, who said the group was “pledged to run a 100 percent positive campaign” for Sanders.

Sheyman also announced that, “regardless of who wins the nomination, MoveOn will support the eventual Democratic nominee in the general election to keep a Republican out of the White House, because the vast majority of members have made clear that it’s what they want MoveOn to do.”