Sen. Elizabeth WarrenElizabeth Ann WarrenBipartisan group of lawmakers aim to reform US sugar program Schumer: Dems want DACA fix in government spending bill The Hill interview — DNC chief: I came here to win elections MORE (D-Mass.) endorsed a Democrat vying to represent her state’s sixth congressional district — for the second time this election cycle.

The rising Democratic star on Saturday offered her endorsement of Seth MoultonSeth Wilbur MoultonHouse Democrat slams NRA in wake of Texas shooting GOP rep: ATF should re-evaluate bump stocks Dem on UN address: Trump doesn't speak for all Americans 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.