By the time Massachusetts Rep. John F. Tierney knew he had a real primary race on his hands, it was too late.  

The nine-term lawmaker lost Tuesday night to fellow Democrat Seth Moulton, an Iraq War veteran who latched onto frustration with Tierney’s past ethical troubles and an anti-incumbent sentiment to win by a stunning 8-point margin .  

Multiple Democratic operatives in the Bay State and the District say the race shifted quickly in Moulton’s favor in the final week and a half, as voters ended summer vacations, kids returned to school and the electorate as a whole began to finally pay attention to the race.  

By that point, Moulton had been on air for weeks with hundreds of thousands of dollars in advertising that Tierney declined to match. Moulton ran spots painting himself as the more electable Democrat in the 6th District, located in the suburbs and towns northeast of Boston. The region’s biggest newspapers, including the Boston Globe , endorsed Moulton, which he touted in his closing ads as a final sell to remaining undecided voters.  

“It just moved faster than I think anyone thought it would,” said a Democratic operative privy to internal polling in the contest. “It closed quickly, but that’s what a million dollars in unanswered spending does.”  

For much of the race, Tierney brushed off the notion he could be vulnerable to another Democrat.  

“Apparently he missed the last election, where we won,” Tierney said of Moulton in a March interview with CQ Roll Call . “But we’ve had strong backing in this election — people who have stood with us through thick and thin. We expect to win, and to win by a good margin.”  

Instead, Tierney sat on much of his $1.3 million war chest, preparing to unleash it on the GOP nominee, former state Sen. Richard Tisei.  

Democratic operatives say Tierney’s team advised him to take this strategy based on polling from as recent as three weeks ago that showed the incumbent with a double-digit lead over Moulton. They said Tierney’s team encouraged him to save his funds for a general-election rematch with Tisei, whom Tierney beat by a single point in 2012.  

Moulton and his team — including former Democratic Congressional Campaign Committee aide Carrie Rankin and Democratic operative Joe Trippi — used more than $1 million to convince Democratic voters they had another choice, one with an even better shot of keeping the seat in the party’s column.  

“Everyone rallied to him two years ago to keep the seat,” Mary Anne Marsh, a Massachusetts Democratic operative, said of Tierney. “Then Seth gave them a choice, and they wanted a fresh face and a fresh start.”  

In the final 10 days of the race, Democratic operatives said it became clear that message was helping close the gap.  

A trio of automated
polls conducted in early September and released in the final days of the race showed Tierney with low single-digit leads, all within the margin of error. The polls were largely dismissed because two of them came from untested pollsters with little to no track record in Massachusetts.  

Yet there was a clear sign Tierney’s campaign saw the shift, too.  

In the last week of the contest, Tierney aired an attack ad, trying to tie Moulton to a group that donates to GOP candidates. It aired at halftime of the New England Patriots’ first game of the season — a heavily watched program, but a pricey block of TV time.  

“Clearly there was just a ton of movement,” said another Democratic strategist. “We saw no signs of it back then, but obviously when you saw Tierney going negative, you knew something was moving here.”  

No matter how the shift happened, Tierney’s loss changes the calculus in a top target for Republicans.  

A scandal surrounding a gambling ring run by Tierney’s brother-in-law dogged the Democratic congressman in 2012, and it made him uniquely vulnerable in a seat Democrats wouldn’t otherwise sweat over. President Barack Obama won here in 2012 by 11 points.  

Democrats now argue Moulton makes the race more difficult for Republicans. The only record the 35-year-old Harvard-educated marine has is his military service, in which he was close to retired generals David Petraeus and Stanley McChrystal. It’s not what the GOP was preparing for this fall.  

Moulton does start the race with one significant disadvantage: His war chest is likely depleted. As of Aug. 20, Moulton reported $481,000 in cash on hand, a total he almost certainly dipped into in the final days of the race.  

Tisei, on the other hand, reported $754,000 as of the same date. The Republican is well-known and well-liked in the district after his 2012 bid against Tierney. He’s an openly gay Republican who has built a profile as a moderate consensus builder .  

That’s why Democratic operatives say they are unlikely to take the race for granted and will help boost Moulton in the home stretch. The Democratic Congressional Campaign Committee has reserved  millions  in TV time there. House Majority PAC , a Democratic super PAC, has also reserved about $1.88 million here.

Roll Call Election Map: Race Ratings for Every Seat


Could John Tierney Lose His Primary? 


John Tierney Survived 2012. Now What?


Gay Republican Candidate ‘Comfortable’ in GOP (Video)


Tierney Primary Challenger: I’m Being Encouraged to Run (Video)


Casualty List: 113th Congress


Get breaking news alerts and more from Roll Call in your inbox or on your iPhone.