TRENTON -- Gov. Christie has antagonized New Jersey's largest teachers' union since he took office in 2010, once declaring on television that the national organization deserved a punch in the face.

The union has struggled under Christie's eight-year governorship, but as the Republican prepares to leave office next year, the New Jersey Education Association is punching back at someone it sees as Christie's chief collaborator: Senate President Stephen Sweeney.

"We're looking for a new governor and a new Senate president," Wendell Steinhauer, the group's president, said in an interview.

The union is considering all possible options to defeat Sweeney, Steinhauer said: backing a primary challenger or a Republican in a general election, or supporting a challenger in a Senate leadership fight.

Although the union may have the money to make Sweeney (D., Gloucester) sweat, a move to unseat him or intervene in a party leadership election risks considerable backlash at a time when the teachers need friends on pressing issues such as pension reform and school funding. Whatever the outcome, it'll be a test of the union's strength after the Christie years.

The stakes are high, given that the Senate president is one of the most powerful political positions in the state.

Given Sweeney's campaign largesse (he had $861,000 in the bank as of January), potential backing from multiple super PACs capable of raising millions of dollars, and the support of childhood friend George E. Norcross III, perhaps the most effective political operative in the state, it would be extraordinarily difficult to beat him in a primary or general election.

At a minimum, the union is focused on blocking Sweeney from another term as Senate president.

"Outside organizations can get involved" in leadership fights, said State Sen. Raymond J. Lesniak (D., Union). "But normally they do it discreetly, if you will. It could backfire on them."

This effort is anything but subtle. The teachers' union launched a website, called Change NJ Politics, that declares: "Working with Chris Christie, Sen. Sweeney betrayed our trust and broke his promises." The site encourages lobbying Third Legislative District members to "join the canvasses in their area as we talk about changing their legislative representation."

On Twitter, the union uses the hashtag #CantTrustSweeney and posts links to opinion articles critical of the Senate president.

It's the kind of attack Trenton observers anticipated that Sweeney, once considered among the front-runners for the Democratic gubernatorial nomination, would face in a statewide primary this year.

Sweeney, a former Gloucester County freeholder director, has held elective office since 1997 and represented the Third District in the Senate since 2002. He has never lost an election. In 2007, he rose to majority leader and two years later, topped longtime Democratic leader Richard J. Codey to become Senate president.

Since deciding against a gubernatorial run in October, Sweeney has tried to lock in support for another term as Senate president -- a leader picked by the majority party in the Legislature immediately after an election. He's won endorsements from a number of state senators. And his South Jersey power base may well expand in November with the retirement of Republican Sen. Diane Allen of Burlington County. A Democrat, likely Assemblyman Troy Singleton, is expected to pick up the seat.

In recent days, Sweeney also has rolled out reelection endorsements from such popular elected officials as U.S. Sen. Cory A. Booker, influential building trades unions, and Phil Murphy, the front-runner for the Democratic gubernatorial nomination who has been endorsed by the teachers' union.

The union, which represents more than 200,000 teachers and other members across the state, is a force in its own right. It has 13 lobbyists in Trenton, according to records filed with the Election Law Enforcement Commission. In the 15 years ending in 2014, it spent double any other interest group.

The union has gone after a Senate president before: Democrat John Lynch in 1991. He narrowly won reelection in a bad year for his party.

The union points to three chief perceived transgressions by Sweeney: his shepherding of a 2011 law that forced public workers to contribute more toward their pensions and health benefits; his failure to hold Christie "accountable" for underfunding schools; and his refusal to hold a vote last summer on a measure that would make pension funding a constitutional requirement.

Amid debate over the proposed constitutional amendment, Sweeney accused the teachers' union of extortion and urged federal and state authorities to investigate the matter.

Through a spokesman, Sweeney declined to comment for this article.

To be sure, the union has picked fights with Sweeney before. During the heated debate over the 2011 pension and health benefits legislation, the union, under different leadership, launched a TV ad that suggested Sweeney was trying to line the pockets of Norcross, a South Jersey insurance executive.

Norcross and others, including Booker, then the mayor of Newark, called the ad campaign disgraceful. Norcross and his South Jersey Democratic machine later reached a detente with the union's new leadership, deciding they were better off working together.

But this fight is different, political observers say.

In screening interviews as part of its endorsement process, the union has asked Senate candidates whether they plan to support Sweeney for Senate president, according to people familiar with the matter.

That, coupled with the union's public campaign against the Senate president, is forcing upon Democrats a loyalty test that could engender resentment toward the teachers.

"If there's one vote that incumbent legislators make that's more jealously guarded than anything else, it's the ability to pick their own leaders," said Carl Golden, who was press secretary for two Republican governors. "That's been proven time after time after time."

"Are the Democrats going to say, 'Well, we don't pick our leaders, the NJEA does?'

"The optics of that are not particularly complimentary," he added.

Governors have also tried to intervene in leadership elections; they usually regret it. After Christie won a landslide reelection in 2013, but Republicans failed to make gains in the Democratic-controlled Legislature, the governor, then at the peak of his power, tried and failed to oust Tom Kean Jr. from his post as Senate Republican leader.

The teachers' union is betting it holds more sway. From 1999 to 2013, it spent $57 million on lobbying, campaign contributions, and independent expenditures -- twice as much as any other interest group, according to the Election Law Enforcement Commission.

Asked how much money the union was willing to spend to defeat Sweeney, Ginger Gold Schnitzer, the group's top lobbyist, said: "Exactly what's necessary to get the job done and not a nickel more."