Sen. Elizabeth WarrenElizabeth Ann WarrenSenate Dems introduce bill to prevent Trump from using disaster funds to build wall Klobuchar, O'Rourke visit Wisconsin as 2020 race heats up Sherrod Brown pushes for Medicare buy-in proposal in place of 'Medicare for all' MORE (D-Mass.) endorsed a Democrat vying to represent her state’s sixth congressional district — for the second time this election cycle.

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The rising Democratic star on Saturday offered her endorsement of Seth MoultonSeth Wilbur MoultonDem lawmaker: 'Trump's presidency is the real national emergency' The Hill's Morning Report - Presented by the American Academy of HIV Medicine - All eyes on Trump after lawmakers reach spending deal Overnight Defense: Acting Pentagon chief visits Afghanistan | US, Taliban peace talks intensify | Trump tweets in Persian to send message to Iran | Defense world pays tribute to Walter Jones MORE, the Marine veteran Democrat who will face off against Republican businessman Richard Tisei in November.

That wouldn’t be unusual, except Warren had already endorsed a Democrat in the race: incumbent Rep. John Tierney (D-Mass.). Moulton surprised the nine-term lawmaker in the Democratic primary earlier this month, buoyed by high-profile endorsements including that of retired Army Gen. Stanley McChrystal, the former top U.S. commander in Afghanistan.

At a campaign event at a Massachusetts restaurant, Warren sang the praises of her party’s new nominee.

"I didn't win an election by myself. We did this together. We magnify our voices and make each other stronger in fighting for the values that we share,” Warren said. “I endorse a man who fights for our values every single day -- Seth Moulton all the way!"

The endorsement should help bolster Moulton’s lead in the race. A WBUR poll released Friday shows the Democrat with a 47-39 percent advantage in the race. Both candidates had identical favorability numbers - 42 percent - but Moulton appears to have the advantage in the lean Democratic district.