More than 40 years ago, top leaders of both parties fell into an early-morning routine on days when the Legislature met in Trenton.

Around 8:30 a.m., Democratic leaders met with Gov. Brendan T. Byrne, who would "tell them what he wanted to do and they would tell him what they were going to do or not do,'' recalled Thomas V. O'Neil, who served as Byrne's legal counsel to the legislature.

After 20 minutes or so, the Republican leaders joined them. It was basic diplomacy, a strategy Byrne learned from his days as a young counsel in Gov. Robert Meyner's office in the 1950s.

These sessions did not become bipartisan group hugs, nor did they yield immediate political breakthroughs, but they kept the channels open and prevented personal animosity from boiling into the public. And sometimes — as in the battle to create the state income tax in 1976 — the talks helped pry away a few important Republican votes.

"Even though there were resentments, there was always a dialogue,'' said O'Neil, who later became a lobbyist.

That almost quaint notion of dialogue and occasional cooperation stands in stark contrast to modern Trenton, now engulfed in one of the nastiest intraparty feuds in state history. The battle, which scuttled the push to legalize recreational marijuana, also threatens to derail the rebuilding of the state's mass transit agency and bring state government to another shutdown this summer.

But this is not just a short-term political squabble. This is a power struggle over the heart of the Democratic Party, which dominates the Statehouse. Will it remain a party controlled by a confederation of transactional party bosses, or will a new-guard coalition of public employee unions, grassroots liberals and activists who have coalesced behind Gov. Phil Murphy take control of the agenda?

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Instead of closed-door dialogue, Murphy and his closest allies have raised millions to clobber fellow Democratic leaders, although not by name, as toadies of President Donald Trump and former Republican Gov. Chris Christie for opposing Murphy's plan to raise taxes on millionaires.

"Trump and Christie promised their tax cuts would help the average New Jerseyan when they knew that wasn’t true,'' reads the digital petition distributed Monday by New Direction New Jersey, the Murphy-aligned "dark money" group funded by secret donors.

It's the kind of hardball more commonly seen in the homestretch of a nasty, neck-and-neck campaign, not in the homestretch of budget negotiations, and especially not between leaders of the same party.

It seems Trenton has plunged into a dark, uncharted no man's land, where there is no script or political history to turn to for guidance or comfort. Murphy and Senate President Stephen Sweeney, D-Gloucester, are locked in a bitter, personal war that has left the Statehouse nervous and wondering where it all leads.

In the past, these kind of bitter feuds evolved into a predictable Trenton kabuki, public political theater that disguised the more sober, pragmatic and private negotiations over a state budget that must be signed into law before a constitutionally mandated deadline of July 1.

Murphy launched the first salvo this winter, vowing to restructure the state's program of doling out tax credits to retain or lure companies to New Jersey.

Prompted by a state comptroller's critical report, Murphy assembled a special panel of white-collar lawyers to investigate the program, which quickly targeted nearly $1.1 billion of incentives awarded to businesses and allies connected to Democratic power broker George Norcross and his brother Philip, leader of an influential law firm.

Sweeney, a childhood friend and political ally of George Norcross, shepherded through a 2013 law that was revised in the final hours before passage to benefit Camden, the heart of the Norcross political turf.

The panel's work prompted the normally behind-the-scenes Norcross to publicly lash out at Murphy with surprising vitriol, accusing Murphy of smearing his family's name and comparing Murphy and his wife, Tammy, to the king and queen of England.

In interviews, Norcross has depicted Murphy as a liar and an incompetent, and has assembled a team of top-shelf lawyers to stop the inquiry.

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Murphy has largely chosen an above-the-fray approach. His staff denies that the panel is obsessed with Camden and claims its goal is to reform a program that has sent $11 billion in tax breaks down a "black hole" of abuse and waste.

But a reported state grand jury subpoena issued last week to the Economic Development Authority, which administers the tax incentives, has ratcheted up the political tension.

Sweeney and Assembly Speaker Craig Coughlin, who voted for the millionaire's tax in the past, now vehemently oppose it, setting the stage for another government shutdown this summer.

Meanwhile, Murphy is vetoing bills with assembly-line regularity, 65 since taking office, or one fewer than Christie during his first term, according to Sweeney's count.

With such bitter enmity, lawmakers are bracing for an uncertain, rough ride into the summer. Last year, Murphy was forced to settle for a limited tax hike on earners of $5 million or more. But this year, Murphy appears more determined to leg it out, regardless of the fallout.

"Nothing is going to happen until this feud is settled,'' said Assemblyman Ralph Caputo, D-Essex.

Some of Murphy's advisers believe the public will stand by him through the thick of a shutdown battle as he frames it as a fight for the middle class against the protectors of a small number of millionaires. Yet Murphy has few loyalists in the Legislature who want to publicly wage war against the Sweeney-Norcross machine.

And despite New Direction's web and television campaign, few Trenton veterans believe that kind of publicity will lead voters to storm their local legislator's office demanding a tax increase on millionaires.

A more likely scenario is that voters will blame Murphy, the state's most visible and powerful politician, if state offices, beaches and parks are closed in early July.

As it stands, the leaders are barely talking to each other. Asked Monday about the millionaires tax and Sweeney's refusal to consider it, Murphy said he reached out to Sweeney last Friday and left a message on his phone, arguing that the hike is "the right thing to do" for the middle class and "those who dream to look up and one day get there."

To Statehouse veterans who honed their skills when the mimeograph and fax machine were cutting-edge technologies, Murphy, the former U.S ambassador to Germany, is flouting other rules of diplomacy and the hard work needed to forge relationships in Trenton.

O'Neil recalls how Byrne insisted on avoiding vetoes or conditional vetoes, and urged his staff to take a nip-it-in-the-bud approach with lawmakers and leaders. That meant identifying and smoothing out trouble spots earlier in the legislative process.

"Byrne said, 'If we have to veto anything, that means you failed to successfully communicate our position in advance to the Legislature,' '' O'Neil said.

Murphy is the new-age guy. He's communicating on the web and television, relying more on big donor dollars than staff. And he's going directly to the public. It's a political strategy that doesn't require regular morning meetings in Trenton.