At a 40th-birthday party in July for Franklin Foer, editor of the New Republic, the magazine’s young owner, Chris Hughes, got all choked up as he pledged to the roomful of writers at Foer’s country home in Pennsylvania that the two would be “intellectual partners for decades.”

But the moist-eyed Hughes would, in the coming months, prove himself to be neither an intellectual nor a partner but a dilettante and a fraud.

When he bought the magazine in 2012 at the age of 28, the Facebook co-founder pledged to “double down” on “in-depth, rigorous reporting,” telling NPR that “the demand for long-form, quality journalism is strong in our country.”

But after just two years, Hughes decided that saving long-form journalism was just too hard. He declared that the 100-year-old journal of opinion would become a technology company, and he brought in a new CEO who literally proposed that writers team up with engineers to make “widgets” for TNR’s Web site.

Hughes ousted his intellectual partner Foer without even the courtesy of telling him; Foer found out when his replacement, a man who previously had been fired as editor of the gossip Web site Gawker, began announcing himself as the new editor and offering people jobs. Most of the staff quit in protest, and the Hughes management team suspended publication until February. They needn’t bother resuming at all. The New Republic is dead; Chris Hughes killed it.

This is personal for me. I left the Wall Street Journal to join TNR in the 1990s, taking a 50 percent pay cut and a 95 percent reduction in subscribers for the pleasure of joining what felt like a family. I met Hughes earlier this year, and I, too, was fooled by his talk about the resources he was pumping into the magazine. I told him in an e-mail that he was “doing the Lord’s work in rescuing this proud old brand” and called him a “21st-century Walter Lippmann.”

But Hughes is no Lippmann; he’s a callow man who accidentally became rich — to the tune of some $700 million — because he had the luck of being Facebook founder Mark Zuckerberg’s roommate at Harvard. Hughes seemed intent on proving he could be a success in his own right, but it hasn’t happened. He created a “cause-oriented social network,” Jumo, in 2010, but when it didn’t take off, he was done with it in 2011. He turned out to be no more devoted to TNR.

He began with a flourish, rehiring Foer, a well-liked former editor, for the top job. He spent lavishly, opening and staffing a New York office and moving the Washington office to glitzy new quarters with big windows overlooking the National Portrait Gallery. He hired an interior decorator to advise him on office decor, and he picked out the paint colors himself. Hughes built a library for Leon Wieseltier, then TNR’s legendary literary editor, and insisted that it be painted the same color as the bedroom in one of Hughes’s three homes.

He said all the right things, telling the New York Times that he would “recruit a lineup of all-stars” and put the magazine in a league with the New Yorker. He was still on message last year, telling Pando that “we are not the next big trend in Silicon Valley.” And Foer got good results for Hughes: a succession of high-impact stories, and online readership that was on course to double to 6 million this year from 3 million in 2013.

Hughes is no idiot (he reads Balzac in French), but as a businessman he turned out to be a lost boy. When he took over in 2012, he fired the magazine’s business staff, hiring instead a Harvard friend with no media experience. He had no interest in the work needed to woo advertisers. He redesigned the Web site himself; it looked good but didn’t work well. He tried to eliminate land-line phones, seeing no reason why reporters might need them. And his spending spree caused annual losses to swell from $1 million when he bought the struggling magazine (he was its fifth owner in a decade) to $5 million.

While his mistakes are excusable, his childish impatience is not. After David Bradley bought the Atlantic in 1999, he made plenty of mistakes — but he kept the long view and ultimately made that grand old institution a leader in digital innovation. By contrast, Hughes became bored with journalism, occupying himself with the latest phones and the prospect of creating new apps; his visits to Washington headquarters became infrequent. He announced a “New Republic Fund” to invest in “early-stage technology companies.”

The final blow: bringing in former Yahoo News general manager Guy Vidra (who once worked on the business staff of The Post) to be CEO, a man dedicated to “re-imagining TNR as a vertically integrated digital media company.” And Hughes became bitter. In its Oct. 31 edition, the New York Times published an article about his husband, Sean Eldridge, who was running for Congress in Upstate New York “with a thin résumé and a thick wallet.” Eldridge and Hughes bought a house in the district in 2013 for $2 million, though it was just an hour from the $5 million home they already owned.

The same day the article appeared, Hughes lashed out in a group e-mail to staff because senior editor (and former Post reporter) Alec MacGillis had dared to propose writing a piece about Apple avoiding taxes just after Apple’s Tim Cook had come out of the closet. Hughes shot back that “Apple has acted squarely within the law” and that MacGillis’s argument would be “tone deaf.” MacGillis quickly backed off, but Hughes did not, writing twice more to defend Apple’s tax strategy and to call Cook “incredibly heroic” for coming out.

After Hughes’s husband lost by 30 points in what should have been a close race in a swing district, it became an open secret that Hughes was done with the New Republic. At a lavish 100th-anniversary gala for the magazine at the Mellon Auditorium on Nov. 19, Hughes did the seating chart himself — and he put most of the magazine staff at tables in the back. He told junior staffers they could not bring guests to the event, and he reacted furiously when one politely asked if she could bring her fiance, who had given the magazine pro bono advice on social-media strategy.

Two weeks later, Foer, after learning of his firing secondhand, called Hughes, who claimed, absurdly, that it was “Guy’s decision.” In a Hughes op-ed published by The Post on Sunday night, after the staff walkout and withdrawal of articles by outside contributors forced him to suspend publication, Hughes said that the New Republic should “become a sustainable business and not position ourselves to rely on the largesse of an unpredictable few.”

An unpredictable few? The magazine relied on an unpredictable one — him — and he failed it.

R.I.P., TNR. You deserved better than Chris Hughes.