WASHINGTON — The White House press secretary, Sean M. Spicer, has taken to slapping journalists who write unflattering stories with an epithet he sees as the epitome of low-road, New York Post-style gossip: “Page Six reporter.’’

Whether the New England-born spokesman realizes it or not, the expression is perhaps less an insult than a reminder of an era when now President Trump mastered the New York tabloid terrain — and his own narrative — shaping his image with a combination of on-the-record bluster and off-the-record gossip.

He’s not in Manhattan anymore. This New York-iest of politicians, now an idiosyncratic, write-your-own-rules president, has stumbled into the most conventional of Washington traps: believing he can master an entrenched political press corps with far deeper connections to the permanent government of federal law enforcement and executive department officials than he has.

Instead, Trump has found himself subsumed and increasingly infuriated by the leaks and criticisms he’s long prided himself on vanquishing. Now, goaded by Steve Bannon, his chief strategist, Trump has turned on the news media with escalating rhetoric, labeling major outlets as “the enemy of the American people.’’

On Saturday afternoon, Trump declared on Twitter that he would not be attending the annual White House Correspondents’ Association Dinner, in April. The event is typically hosted by a comedian who roasts the president, along with the president roasting the press.

Trump’s acrimonious relationship with the media is a sharp break from previous presidents — and from his own comfortable three-decade tango with the tabloids.

“New York is extremely intense and competitive, but it is actually a much smaller pond than Washington, where you have many more players with access to many more sources,’’ said Howard Wolfson, who has split his career between New York and Washington, advising New York’s former mayor Michael R. Bloomberg and Hillary Clinton’s 2008 presidential campaign.

“In New York, you can create a manageable set of relationships in a smaller universe,’’ Wolfson said. “In Washington, that becomes a lot more complicated.’’

There’s another fundamental difference: During his Page Six days, Trump was, by and large, trafficking in trivia. As president, he is dealing with the most serious issues of the day, and it is the role of news organizations to cover them.

Linda Stasi, who chronicled Trump’s up-and-down marriage to Marla Maples in the 1990s for two New York papers, said she could have predicted the presidential agita.

“He would plant stories and he would get mad if they didn’t come out exactly as he wanted,’’ she recalled of earlier dealings with Trump.

The White House, on the defensive last week after a series of missteps and leaked stories, sought to shift to offense, targeting the news media as an enemy, in the absence of any more formidable foil in a city now firmly controlled by Republicans.

Bannon described the “corporatist media’’ as the “opposition party’’ in a Thursday speech.

Then there was Trump’s 10-minute attack on “fake news’’ during his speech Friday at the Conservative Political Action Conference.

Reporters back in New York, however, knew that the president’s call for an end to “sources’’ — meaning anonymous sources leaking damaging details of his campaign’s relationship with Russian officials — didn’t jibe with his onetime role as a no-fingerprints gossipmonger, touting his business dealings and romantic life in late-night phone calls.

“He used to be the one leaking,’’ Stasi pointed out Friday night from her office at The Daily News, where she is now a columnist. “He was leaking about himself. He would call up with fake accents and pretend it wasn’t him. He would tell us 100 times: ‘Now listen, I’m going to tell you something, but it didn’t come from me.’’’

Still, for a sophisticated consumer of news, Trump retains a brutally simple, almost Manichaean view of his coverage: good stories are good, bad stories are evil. It could prove an untenable attribute for the most scrutinized man in the world.