As for Democrats, at the national party’s House campaign headquarters, spokeswoman Meredith Kelly praised Lamb’s “long record of public service to our country.” But the party hasn’t included the district on its official list of GOP-held targets, which now has 91 seats. Democrats must flip 24 GOP-held seats to regain a majority in the House.

In 2017, Democrats managed surprisingly competitive races in four special congressional races in heavily Republican districts, but lost all four.

Lamb must “run a perfect campaign,” said Mike Mikus, a Democratic campaign strategist who has run congressional races in the Pittsburgh area. “But it can be done,” Mikus added.

Registered Democrats outnumber Republicans in the district by about 70,000, a reflection of organized labor’s long influence in the district. But many of those union households embraced Trump’s populist, protectionist message in 2016, and Mikus noted they’re also culturally conservative.

Lamb and Democrats believe they have an opening that wasn’t available before, given that Murphy was among the few Washington Republicans who voted with labor unions and regularly got their endorsements.

This time, the state AFL-CIO has endorsed Lamb, and he is trying to strike the tone Mikus says is necessary for a Democrat to win.

Lamb’s first television ad, set to air Thursday, notes he has refused “corporate PAC money” and believes both parties “need new leaders in Congress.” That’s a reference to his promise to not to back House Democrat leader Nancy Pelosi for speaker. She is unpopular in many districts and the GOP regularly uses her as a cudgel on Democratic nominees.

The 30-second spot also tells voters that Lamb grew up in the district and says he “still loves to shoot.”

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Barrow reported from Atlanta. Associated Press reporters Marc Levy in Harrisburg, Pennsylvania, and Jill Colvin in Washington contributed to this report.

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Follow Barrow on Twitter at https://twitter.com/BillBarrowAP