Ohio Sen. Sherrod Brown, a liberal favorite who stayed neutral in the 2008 Democratic primary, has endorsed Hillary Clinton over his colleague Sen. Bernie Sanders in the 2016 race.

“As Ohio’s working families continue to recover from the worst economic recession in our country’s history, we need a president who’s committed to growing our economy by lifting up the middle class,” Brown said in a statement. “I am proud to endorse her today because I know she will keep Ohio moving forward.​”

It’s another significant nod for Clinton, leaving few remaining possible supporters in Congress for Sanders. Brown is a leading populist progressive in the Senate with close ties to labor unions. And he has worked with Sanders on numerous pieces of legislation.

Sanders so far has only two Democratic members of Congress supporting him, the two co-chairmen of the Congressional Progressive Caucus. And Brown’s support comes a day after Clinton picked up the endorsement of Delaware Sen. Tom Carper, who had said he would support fellow Delawarean Joe Biden if the vice president entered the race.

In his statement, Brown cited Clinton’s opposition to the Trans-Pacific Partnership, a massive trade deal between a dozen Pacific Rim countries that Clinton helped negotiate as secretary of state.

“From opposing unfair trade deals to fighting for a fair financial system, Hillary Clinton has shown she puts working families first. She knows as president that her first job will be creating jobs for the middle class,” he said.

Some liberals have floated Brown as a possible vice presidential pick, noting he could help deliver votes in Ohio, perhaps the single most important general election swing state. Brown did not endorse in the heated 2008 Democratic primary between Clinton and then-Sen. Barack Obama until the party had essentially decided, making his early endorsement of Clinton all the more notable.

New York City Mayor Bill deBlasio, another liberal leader, looks poised to endorse Clinton, whose Senate campaign he managed in 2000. That leaves Sen. Elizabeth Warren as arguably the biggest remaining prize on the left.

Meanwhile, a new Monmouth University poll in Iowa out Tuesday morning shows Clinton has expanded her lead over Sanders. The former secretary of state now has 65% of support, with Sanders at 24% and challenger Martin O’Malley at 5%.