Mass primary Election 2014

Rep. John Tierney becomes the fourth House incumbent to lose a primary this cycle.

Democratic Rep. John Tierney was ousted by primary challenger Seth Moulton in Massachusetts’ 6 th District on Tuesday, shaking up what’s expected to be a competitive general election campaign.

Tierney conceded to Moulton, a first-time candidate and Iraq War veteran, Tuesday evening, POLITICO confirmed. Moulton led Tierney, 51 percent to 40 percent, with 80 percent of precincts reporting, according to The Associated Press.

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Moulton, 35, will face moderate, openly gay Republican Richard Tisei, 52, in the fall campaign. Tisei narrowly lost to Tierney, who’s been plagued by a gambling scandal involving his wife and brother-in-law, in 2012. Although the race is still expected to be close, Moulton backers have argued he’s a better candidate to take on Tisei than the scandal-ridden Tierney.

In prepared victory remarks, Moulton called his win a reflection of voter disgust with Washington gridlock, and he vowed to keep the seat for Democrats.

“I look forward to contrasting our vision with that of Richard Tisei’s, ” he said. “We won’t get fresh thinking and new leadership by sending someone to Washington who was first elected to office when I was just six years old.”

Tisei has already previewed his line of attack against Moulton, arguing that he’s likely to vote the same way as Tierney in Congress. Tisei also plans to pitch himself as a rare Massachusetts voice in the all-but-certain GOP House majority.

But Democrats say that’s a smokescreen — and that Republicans were hoping a weakened Tierney would win.

“Seth Moulton is a compelling general-election candidate who comes without the ethical questions that surrounded Tierney, ” said a Democratic strategist, granted anonymity to discuss the race candidly. “Even Republicans have conceded that they wanted to run against Tierney because they don’t have a case to make against Moulton.”

Tierney’s loss makes him the fourth House incumbent – and first Democrat – to lose a primary this cycle. The others are GOP Reps. Ralph Hall, Kerry Bentivolio and Eric Cantor, who has since resigned. It’s also the first time an incumbent has lost a primary for a Massachusetts House seat since 1992.