When New Jersey lost one of its 13 congressional districts last winter, U.S. Rep. Steve Rothman faced a tough choice: run against an incumbent Republican in a right-leaning district that now included some of Rothman's former turf or square off against a fellow Democrat in a newly formed district that included more than half of his old constituency.

Many Democrats urged him to take on U.S. Rep. Scott Garrett, a Republican with tea party leanings in the Fifth District, where the remapping committee put Rothman's hometown of Fair Lawn, Bergen County. Political insiders acknowledged that it would be a tough race, but some argued that Rothman should fight or fail trying for the good of the party. The National Democratic Party offered Rothman a pot of money for the challenge.

Instead, Rothman chose to take on Democrat U.S. Rep. Bill Pascrell in the redrawn Ninth District, setting the scene for New Jersey's most expensive and acrimonious primary fight. It's one of the most closely watched races in the nation, attracting the participation of heavy hitters such as former President Bill Clinton, who will hold a get-out-the-vote rally for Pascrell in Paterson on Friday, four days before Tuesday's statewide primary.

"These guys, after all, were good friends. They used to come back [from Washington] every Thursday night on Amtrak together," said Ross Baker, a Rutgers University political scientist. "Clearly, Congressman Rothman decided that he did not want to run against Scott Garrett ... and I can understand why."

Pascrell, 75, of Paterson, has challenged Rothman's dedication to the party, arguing that he should have made an effort to grab Garrett's seat for the Democrats. A win would have given the party a 7-5 advantage over the GOP in the state's delegation.

But others in the Democratic delegation admit privately that had they been in Rothman's shoes, they would have done the same thing.

"Nobody expects suicidal banzai charges from the members of the House of Representatives," Baker said. "It would have been a very noble thing for Rothman to have said, 'Sure, I'm going into the lion's den' … but I think the rest of the delegation is sitting there saying, 'There but for the grace of God go I.'?"

Rothman, 59, relocated to Englewood, the Bergen County town where he was once mayor. The new Ninth includes parts of Bergen, Passaic, and Hudson Counties.

He and Pascrell, both elected in 1996, are more alike than different: Their voting records match about 98 percent of the time, said Brigid Harrison, a political science professor at Montclair State University.

So Rothman's strategy has been to paint himself as the more liberal candidate in a very blue part of the state, said Ben Dworkin, director of the Rebovich Institute for New Jersey Politics at Rider University.

"You have to find something to distinguish yourself in a district that's overwhelmingly Democratic," he said.

Pascrell's record is slightly more conservative: He voted to ban late-term abortions, and he supported parental notification for minors who seek abortions. He also voted in support of the Troubled Asset Relief Program, or TARP, a program drawn up in the final days of President George W. Bush's tenure that had the federal government buy assets from banks struggling as the economy turned sour.

During three debates and in the ads hitting mailboxes and airwaves in North Jersey, Rothman has used the issues of abortion rights and the bank bailouts to drive a wedge between himself and Pascrell, who has portrayed himself as a pragmatic Democrat.

Rothman has even gone so far as to paint Pascrell as a closet Republican, showing him alongside presumed GOP presidential nominee Mitt Romney, Republican Gov. Christie, and former GOP House Speaker Newt Gingrich. The ad, which the Newark Star-Ledger's PolitiFact website gave a "Pants on Fire" rating for its inaccurate claims, asserted that Pascrell agreed with Republicans that the wealthy deserve additional tax breaks. The televised spot shows a snippet of Pascrell saying, "Republicans had great ideas, I liked some of their ideas."

But Pascrell wasn't talking about tax breaks for the One Percent: He was talking about trying to find compromise in the health-care-reform law.

"This race really headed into the toilet relatively quickly," Harrison said. "It's so rare that you see people who are so ideologically similar going head-to-head in such a vitriolic and personal race."

Political insiders initially gave Rothman the edge because 57 percent of his previous district is in the newly drawn Ninth, Harrison said. He also has more cash on hand — $1.3 million compared with Pascrell's $700,000, according to the latest federal campaign finance filings.

But Pascrell has a big weapon: Clinton, who is repaying Democrats who endorsed his wife for president in 2008 by showing up to help them win in primaries. Rothman, who was the first of the New Jersey delegation to support then-candidate Barack Obama, has received the endorsement of David Axelrod, one of Obama's top advisers. Obama and Democratic House leaders have stayed out of the Pascrell-Rothman fight.

Clinton is supporting Pascrell in voice — through robo-calls to Democrats in the district — and in person. He has lent his support to at least six other Democratic candidates facing primaries across the country this spring.

Endorsements normally don't matter much when it comes to votes, political observers said. But in a divisive Democratic primary where internal campaign polls show the candidates running neck and neck, it could be enough to energize Pascrell supporters.

"Bill Clinton, because of his stature, is probably more of a game-changer than your average endorsement," Dworkin said. "That's a big weapon for the Pascrell team."

Although the Ninth is grabbing the most headlines in New Jersey, there is also a six-way Democratic primary to select a candidate in the race to replace Donald Payne Sr., who was the state's only African American congressman when he died of cancer in March. Vying for the Tenth District nomination are Payne's son, Donald Jr., who is Newark's council president; State Sen. Nia Gill (D., Essex); Ron Rice Jr., another Newark councilman; Irvington Mayor Wayne Smith; political neophyte Cathy Wright, who is a former AT&T manager; and Dennis Flynn, an Iraq War veteran.

Meanwhile in the southern part of the state, a number of incumbents face challenges on Tuesday: • Democratic U.S. Rep. Rob Andrews faces Francis Tenagli, o a retired social studies teacher from Haddon Township, in the First Congressional District, which includes most of Camden County and parts of Gloucester and Burlington Counties. • In the Second District, Republican U.S. Rep. Frank LoBiondo faces Mike Assad, an Absecon school board member with a tea party bent. Three Democrats are also running in the Second, which spans six counties including farms, the Pine Barrens and Atlantic City. • Republican U.S. Rep. Chris Smith, who has represented the Fourth District for 32 years, will face Terrence McGowan, a former firefighter and police officer from Howell Township, in the primary.

Two Republicans are running in the Sixth District to face Democratic U.S. Rep. Frank Pallone, who is running unopposed, in the fall. Anna Little, former mayor of Highlands and a tea party candidate, will face Ernesto Cullari, a small-business owner from Asbury Park. The Sixth includes parts of Monmouth and Middlesex Counties.

In the race for U.S. Senate, Democratic incumbent Robert Menendez also is running unopposed. State Sen. Joe Kyrillos (R., Monmouth), his party's front-running candidate, faces three primary opponents: Bader Qarmout, a Green Township real estate investor; David Douglas Brown, an inventor from East Brunswick; and Joe "Rudy" Rullo, who owns a green energy business in Beachwood.

Contact Joelle Farrell at 856-779-3237 or jfarrell@phillynews.com or on Twitter at @joellefarrell.