Ahead of Sanders' expected endorsement of Clinton in Portsmouth, New Hampshire, the Communications Workers of America and Congressional Progressive Caucus PAC endorsed Clinton for president on Monday. Also joining those groups: Rep. Barbara Lee, a liberal California lawmaker who refused to endorse Clinton earlier this year.
Clinton and Sanders, after months of at times acrimonious campaigning against each other, will stand on the same stage Tuesday, where the liberal senator is expected to end his campaign and back Clinton.
This trio of endorsements comes as Democratic voters, many of whom were split between Clinton and Sanders, are starting to unify around the former secretary of state.
The Communications Workers of America announced in December 2015
that they were backing Sanders, not Clinton, for president.
"CWA members have made a clear choice and a bold stand in endorsing Bernie Sanders for President," Chris Shelton, the union's president, said at the time, noting that the group was looking for someone "who will break with politics-as-usual and fight for America's working people."
But on Monday, in a statement that did not mention Sanders
, the union touted Clinton as "thoughtful and experienced" and thanked her for standing "with CWA members and pledges her commitment to making life better for working families."
Much of the organized labor world has already backed Clinton and CWA was one of the few holdouts. The CWA endorsement, the group said Monday, comes with activists staffing phone banks and walking battleground neighborhoods.
Likewise, the political action committee of the Congressional Progressive Caucus, a group founded by Sanders, said Monday
that Clinton "shares our ideals and has worked to improve the lives of Americans her entire adult life -- as an activist, a litigator, a First Lady, a Senator, and then a Secretary of State."
"Members of PAPAC unite behind her now, and we will work to ensure Secretary Clinton is the next President of the United States," the group said in a statement posted on their website.
The group also thanked Sanders for "raising critical issues in the course of the campaign."
Lee, a former co-chairwoman of the House Progressive Caucus, said Monday that she was "confident that Hillary Clinton will unite the party around the progressive issues outlined in the platform."
A Pew poll
released earlier this month found that 72% of Democratic voters said they would unify behind Clinton. That number is up from 64% in March.