TRENTON, N.J. >> A teachers union that is typically a reliable Democrat ally is spending millions of dollars to help a Donald Trump-supporting Republican try to unseat New Jersey’s top-ranking Democrat, a union leader himself.

The New Jersey Education Association has spent roughly $4.5 million to try to take out Democratic Senate President Steve Sweeney, who faces a challenge in Tuesday’s election from a former Republican town councilman in a suburban Philadelphia district that narrowly voted for Trump last year.

Sweeney and his supporters have responded by spending nearly $10 million in the race against Fran Grenier. The more than $15 million total spent on the race so far makes it the most expensive state Senate race in state history, according to the Election Law Enforcement Commission.

As voters prepare to choose Gov. Chris Christie’s replacement Tuesday, those in the Philadelphia media market also have been greeted by an onslaught of bitter and misleading or incorrect attack ads from the senate race.

The campaign from the state’s largest teachers union sparked by a dispute over pension payments has also driven a wedge between Democrats and the union, which previously spent millions of dollars to help increase the party’s majorities in the Legislature. The union also supported Sweeney in 2013.

“If Democrats are disappointed that our members did not endorse Steve Sweeney this year, they need to take another look at Sweeney’s record of broken promises,” NJEA President Marie Blistan said.

Garden State Forward, the union’s political group, is airing an ad attacking Sweeney for being “caught spending” $100,000 on dinners and cigars, but the claim leaves out context and appears to get the dollar figure wrong.

The ad relies on a 2011 Associated Press article to support its claim, but that report says Sweeney spent $765 on cigars, $1,118 for dinner at a Washington restaurant and more than $10,000 for political meetings. The group didn’t respond to requests from the AP to explain the discrepancy.

The money came from Sweeney’s Gloucester County freeholder re-election fund, a position he had resigned from. New Jersey election law allows former candidates to keep their accounts open as long as they report on their financial activity, as Sweeney did.

A political group backing Sweeney has spent about $2.6 million so far, according to the election commission.

New Jerseyans for a Better Tomorrow has financed an ad that says Grenier was on the Woodstown council when property taxes went up. The ad misses the fact that property taxes across the state have risen about 2 percent annually and also misses that school boards set property tax rates along with town councils.

The union’s beef stems from Sweeney’s failure to post a vote on a proposed constitutional amendment to require the state to make public pension payments, but the bad blood goes back to a 2010 law Sweeney helped shepherd through that resulted in benefit cuts for the group’s members.

Sweeney said the union threatened to withhold campaign contributions unless the amendment was put on the ballot. The group denied wrongdoing and no charges were brought.

Sweeney, an ironworkers union executive, is confident he will return to Trenton, where he’s served in the state Senate since 2002. He cast Grenier as a bad fit and pointed out that Grenier backed Trump in 2016 and has supported Christie, whose approval rating has dropped to the teens. Sweeney has worked with Christie on issues, including pension reform.

“We’re gonna win,” he said recently during a brief interview in the statehouse parking lot.

Grenier did not return messages seeking comment.

The NJEA says it’s backing Grenier because he better supports its members and has denied being “an arm” of the Democratic Party.

The 3rd District includes parts of Cumberland, Gloucester and Salem counties. In 2016, it voted for Trump by about 2,500 votes. The Republican presidential candidate lost New Jersey to Democrat Hillary Clinton by 14 points.