“Establishment” has got to be the season’s most battered buzz word.

True, there are especially powerful American institutions and individuals. They include lobbyists, financial firms, party leaders, top elected officials, the White House, Congress, titans of new media, moguls of old media, the courts, military, labor unions, industrialists, big campaign donors.

But the commentariat has a way of tossing around the “E word” without defining it. The fuzziness sets in especially when socialist Sen. Bernie Sanders and blustery businessman Donald Trump get the same “anti-establishment” label.

Just Tuesday Robert Reich, an academic and author who was secretary of labor under President Bill Clinton, published a commentary linking the Sanders and Trump candidacies into a “rebellion against the establishment.”

Many citizens distrust the current power scenario. In recent years, the “occupy” movement followed on the heels of the “tea party” phenomenon, and some saw them as related.

Even by Reich’s account, though, “There’s no official definition of the establishment.”

Presumably,” he wrote, it includes “all of the people and institutions that have wielded significant power over the American political economy, and are therefore deemed complicit.”

Jeb Bush, supposedly the GOP’s establishment candidate, has quit the race. Republican Trump comes out of a different establishment. He inherited real estate — the equivalent in New York of oil rights in Texas. He profited from legalized casinos. He drew fame as an autocratic boss on supposedly unscripted “reality TV,” which made big bucks for the networks.

In turn, detractors of Texas Sen. Ted Cruz mock his loans from Goldman Sachs and his Princeton-Harvard pedigree.

On the Democratic side, Hillary Clinton’s spin-meisters would undoubtedly love to convince young voters that Sanders’ quarter-century in Congress and past pro-gun rights positions confer more “establishment” status on him than he’d admit.

David Birdsell, dean of the Baruch College School of Public Affairs, sees a “certain natural appeal in draping the same label around both men,” since both are “reframing the political process” by bringing in new, active groups of supporters.

But, he noted, Sanders is committed to expand government’s role if elected while Trump could be expected to reduce it based on his vows of dramatic tax reductions.

As a tactic, the effort to “insider up” one’s political opponent extends to local campaigns. Witness the special-election fight for the Senate seat drawn and later vacated by convicted ex-Majority Leader Dean Skelos.

One contender, Assemb. Todd Kaminsky (D-Long Beach), has served for close to 14 months; his GOP opponent, Chris McGrath, has never been elected. So Republicans are targeting parts of Kaminsky’s record in office while Kaminsky & Co. depict McGrath as a new agent of the Senate’s old status quo.

Candidates sought “anti-establishment” status, deservedly or not, long before the term caught on.

Democrat John P. O’Brien served as New York City mayor for one year, 1933. While campaigning, he assumed an independent posture. But when asked after his inauguration who his police commissioner would be, O’Brien famously replied: “I don’t know. They haven’t told me yet.”

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