Voter turnout Tuesday in New Jersey was the lowest for a general election in state history, according to unofficial results and an analysis by a polling expert.

Against that backdrop, Democrats, who control both chambers of the Legislature, expanded their majority in the Assembly by as many as four seats. Democrats sought to portray their gains as an indictment of Republican Gov. Christie, while the GOP argued it was up against a behemoth of a special-interest group that spent millions of dollars raised by the state's largest teachers' union.

With Assembly races topping the ballot for the first time since 1999, about 21 percent of registered voters cast ballots, said Patrick Murray, director of the Monmouth University Polling Institute. Some counties had not finished reporting election results when Murray completed his analysis, but he predicted the number would not be higher than 22 percent.

The previous low was 25 percent, for the October 2013 special election for U.S. Senate won by former Newark Mayor Cory Booker.

Turnout for legislative races is "always lower than any other election, particularly when it's only the Assembly," Murray said. Swing voters don't make it to the polls when the elections seem preordained because of the way districts are drawn, he added.

Murray noted that turnout has been declining over time, too.

In 2011, when state Senate elections topped the ballot, 27 percent of registered voters cast ballots.

In South Jersey districts on Tuesday, turnout ranged from 20 percent in Camden County to 24 percent in Gloucester County, according to unofficial county data.

Low turnout may have contributed to upsets Democrats appeared to notch in Monmouth County's 11th District, where they ousted two incumbent Republicans, according to unofficial results.

Provisional ballots were still being counted in the 16th District, where Democrat Andrew Zwicker, a Princeton physicist, led incumbent Republican Donna Simon by 29 votes.

In South Jersey's First District, Democrat Bruce Land ousted Republican incumbent Sam Fiocchi.

As of Oct. 30, General Majority PAC, a so-called independent expenditure group, spent nearly $2 million trying to defeat Fiocchi, according to the group's most recent filing with state regulators.

General Majority spent a similar amount in the Second and nearly $200,000 in the 11th, mostly on attack ads.

"New Jersey voters sent Republican legislators a clear message that it is time to focus on New Jersey's needs and not on protecting the governor's right flank for his presidential ambitions," Senate President Stephen Sweeney (D., Gloucester) said in a statement Wednesday.

"It is no accident that the biggest surprises came in the 11th and 16th Districts, where the focus was standing up to the administration and for New Jersey on gun-safety legislation," Sweeney said.

Bill Palatucci, a top adviser to Christie, said, "Their premise doesn't hold up because none of their advertising was anti-Christie. The results yesterday were as expected in a midterm election following the current legislative map, which is rigged for Democrat candidates."

The Senate, with support from three Republicans, recently voted to override Christie's veto of a bill that would make it more difficult for certain individuals with a history of mental illness to expunge such records for the purpose of obtaining a firearm.

Assembly Speaker Vincent Prieto (D., Hudson) has said he will hold an override vote next month.

Republicans said there was little they could do to compete with the New Jersey Education Association, whose allied super PAC donated $3.5 million to General Majority PAC.

General Majority had spent nearly $4 million through Oct. 23 - more than the $3.2 million all Republican candidates combined had spent, according to an analysis by the Election Law Enforcement Commission. Democratic candidates had spent nearly $9 million.

"There was incredible resistance to any more reforms in the state, so you saw millions of dollars" raised by the teachers' union, "and there was only one place to put it: Assembly races," said Minority Leader Jon Bramnick (R., Union). "We were the only game in town."

More broadly, he added, the party of a second-term governor tends to lose seats in the Legislature.

Bramnick rejected the notion that Christie, whose favorability ratings in the state have dipped below 40 percent, was culpable for GOP losses.

"We're really strongly in favor of reforms," he said, "and there are entities in this state that will do anything to stop a reform agenda. I don't think it's a Chris Christie issue."

For its part, the NJEA said Tuesday's results showed "there's no such thing as a safe seat for a legislator who makes a promise but doesn't keep it."

The union had made funding the pension system for public workers its top issue after Christie underfunded the plans, despite a 2011 law that required the state to contribute more.

The state Supreme Court in June struck down a provision in the law that granted public workers a contractual right to pension funding.

"NJEA made no secret of the fact that we were going all in to elect candidates who support upholding the law and making the fiscally responsible decision to fund public employees' pensions," union president Wendell Steinhauer said in a statement.

Christie, who is seeking the GOP presidential nomination, says the pension and health benefits systems are unsustainable and must be changed.

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