Sen. Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.) is set to square off against Republican Geoff Diehl, who was President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE’s campaign co-chairman in Massachusetts, in the state's Senate race.

Diehl, a state representative, emerged the winner in the deep-blue state's Republican primary, The Associated Press projected. He won with 55 percent of the vote, defeating wealthy business executive John Kingston and Beth Lindstrom, a former aide to Gov. Mitt Romney Willard (Mitt) Mitt RomneySenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R).

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Warren, who faced no primary challenger, is the favorite to win a second term in November.

Trump lost Massachusetts by 27 points in 2016. The Massachusetts congressional delegation consists entirely of Democrats, though the state has a popular Republican governor, Charlie Baker, who’s also expected to win reelection this fall.

But Republicans see the Senate race as an opportunity to take hits on Warren, a progressive stalwart and antagonist to Trump, ahead of a potential presidential campaign.

Warren has repeatedly dismissed rumors of a 2020 run, saying that she’s focused on her reelection race this year.

If she decides to mount a bid, Warren would likely face a crowded Democratic primary for a shot at unseating Trump.

Diehl, who’s been a state legislator since 2011, wasn’t the top fundraiser, but had won the Massachusetts Republican Party’s endorsement at its convention in late April.

He also played up his strong ties to the president — something that his opponents seized on by arguing that it would make him unelectable against Warren in November.

Republicans haven’t won a Senate race in the state since 2010, when Scott Brown won the special election to fill the late Sen. Ted Kennedy’s (D) seat. In 2012, Brown lost the race for a full term to Warren.

Warren has a hefty campaign account with nearly $16 million on hand.

Warren, a former Harvard University law professor, was instrumental in creating the Consumer Financial Protection Bureau.

She has also repeatedly clashed with Trump since he took office, grilling his Cabinet officials at hearings. Trump, in turn, has taken aim at Warren during his campaign-style rallies, repeatedly referring to her by a pejorative nickname based on her claims to Native American heritage.