Sen. Elizabeth WarrenElizabeth Ann WarrenKamala Harris will no longer accept corporate PAC money Pompeo faces pivotal vote Dem senators demand Trump explain ties to Koch brothers 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 MoultonLawmakers rip Trump for not seeking congressional approval for Syria strikes Five lawmakers facing tough primary races Democrats lay into Trump's pick of Bolton for national security adviser 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.