Primary season may be waning, but there’s still a nail-biter of a contest in the Northeast, where incumbent Democratic Rep. John Tierney is facing a formidable primary challenge from Iraq vet Seth Moulton.

Despite the fact that he’s a Democrat running in cobalt Massachusetts, Tierney, now in his ninth term in Congress, is one of the cycle’s most vulnerable incumbents. Running down-ballot from President Obama and then-candidate Elizabeth Warren in 2012, Tierney squeaked by with 48 percent of the vote, defeating Republican challenger and former state Senate Minority Leader Richard Tisei by just 3,650 votes.

Tisei is back for round two, but Tierney must defeat a surprisingly agile primary challenger before that can happen. The incumbent Democrat’s opponent just won the ringing endorsement of the Boston Globe, which cited his military experience.

“Moulton’s work in Iraq — negotiating with warlords, developing on-the-ground relationships in tense circumstances — might bode well for his ability to deal with recalcitrant Republicans, and to broker agreements between the two parties,” wrote the paper’s editors.

And retired Gen. Stanley McChrystal recently endorsed him as well — his first endorsement ever, per The Hill. Moulton’s work as a top aide to former U.S. commander David Petraeus may have given him an edge for courting powerful members of the military.

Election Day is Tuesday.

CORRECTION: This story originally ran with an incorrect photo. The Washington Examiner regrets the error.