If nasty campaign rhetoric is a contagious disease, the Star-Ledger of Newark, N.J., and the New Hampshire Union-Leader appear to have contracted it.

The Union-Leader endorsed New Jersey Gov. Chris Christie for president over the weekend, calling him “the one candidate who has the range and type of experience the nation desperately needs.” Newspaper editorial boards make endorsements all the time, but the Union-Leader’s backing is a big deal because, historically, it has been followed by a boost in the state (though not necessarily a primary victory) for the candidate.

Anyway, the endorsement so appalled Tom Moran, the editorial page editor of the Star-Ledger, that he called up his counterpart at the Union-Leader, Grant Bosse, to essentially ask what on Earth he was thinking. Their conversation led to a column on Monday in which Moran asserted that the Union-Leader “knows almost nothing about [Christie’s] record as governor.”

“I hate to second-guess a fellow editorial board,” Moran wrote, while also calling Bosse “a very nice guy.” Nevertheless, he ripped the Union-Leader for overlooking the Bridgegate scandal (which the Star-Ledger covered extensively), as well as what Moran considers Christie’s poor record on pension reform, hurricane relief and job creation.

Bosse fired back in an appearance on MSNBC, saying that “at this point, the Star-Ledger is Chris Christie’s crazy ex-girlfriend” — a reference to the fact that the New Jersey paper previously endorsed Christie for governor.

“Now, they’re going around town bad-mouthing anybody that he takes out to dinner,” Bosse said.

The episode is highly entertaining — and unusual. Newspapers generally make their own endorsements without knocking the decisions of others.

But what’s most striking about the feud is the way in which it resembles the intra-party bickering of a primary campaign, in which rivals exchange personal platitudes, shred each other on policy, then ultimately resort to name-calling when things get heated.

The “crazy ex-girlfriend” line even has a Trump-like quality to it. In fact, when MSNBC’s Chris Hayes asked Bosse whether he “really want[s] to stick with that metaphor” — presenting a chance to tone things down a bit — Bosse made like Trump and doubled down.

“Yeah, they’re just going around saying bad things,” he replied.

Maybe this is a smart move. It’s working for Trump, right?

But it’s also the sort of behavior that often frustrates voters, who wonder why candidates can’t keep their disagreements more civil. And for a press corps that’s here to cover the fray, not join it, it’s probably not the kind of thing you want to emulate.