"They are meddling in a Republican primary with the hopes of propping up Steve Lonegan and dragging him across the line next week so they can beat him in November," said Chris Russell, a spokesman for MacArthur, a former insurance executive, who has put more than $2 million of his own money into the race.
Said Lonegan spokesman Tim Kelly: "It's no surprise they are attacking Steve Lonegan. He's the only conservative in this race and the only candidate who has won in this district."
The two are running in a district that includes much of Burlington and Ocean Counties, where GOP leaders fear that a far-right approach might be a liability in the fall.
As Republicans around the nation have battled internally over the direction of their party, Democrats have reaped the benefits of upsets in which more conservative - but less polished - candidates have defeated mainstream picks. At times, Democrats have worked to help make such upsets happen.
Patriot Majority also stepped into North Carolina's GOP Senate primary earlier this year, attacking the party-establishment favorite in the hopes of aiding an endangered Democrat, Sen. Kay Hagan. (The establishment candidate won.)
"Clearly, Democratic groups are trying to game the system so that they can get a better opponent," said Kathy Kiely, managing editor of the nonpartisan Sunlight Foundation, which tracks money in politics. "This is an age-old tactic. It goes way back."
The most notorious recent example was the 2012 race in which Sen. Claire McCaskill (D., Mo.) ran ads criticizing GOP candidate Todd Akin for being too conservative. Akin won the Republican primary, uttered the infamous phrase legitimate rape - and helped McCaskill to an easy win in what was supposed to be a tough race or GOP victory.
Kiely said ads such as those now appearing in the South Jersey race point to the need for greater transparency. "Unless you're a political junkie . . . you wouldn't know that Patriot Majority is a Democratic group," Kiely said.
Patriot Majority - which features an image of a Revolutionary War soldier on its website and has 1776@PatriotMajority.org as its e-mail address - at first looks like many tea party groups (though its website makes its leanings clear).
Its president, Craig Varoga, has previously worked on the Democratic presidential campaigns of Bill Clinton, Al Gore, and John Kerry. Meanwhile, even as the Patriot Majority has attacked MacArthur and Lonegan, other groups watching the race are ready to aid Republicans in more traditional ways.
The American Action Network, a Washington-based group dedicated to supporting "center-right" Republicans, has twice polled on the primary.
Its latest survey found MacArthur leading Lonegan by 13 percentage points among 400 likely Republican primary voters - up eight points since its April survey, according to a summary memo shared with The Inquirer. The new poll has a margin of error of plus or minus 4.9 percent.
The organization's political fund spent $627,000 to help Runyan's reelection in 2012, and it could follow up this fall.
The poll, taken May 18-20 by a GOP firm, the Tarrance Group, echoes what a Monmouth University Poll found days earlier.
MacArthur is the choice of the Republican establishment, which sees him as a more temperate candidate who can appeal to a district that has long supported Republicans for Congress but where Democrats have more registered voters.
Democrats have their own primary Tuesday, between national party pick Aimee Belgard, a Burlington County freeholder, and attorney Howard Kleinhendler.
One Patriot Majority mailer bashes MacArthur for raising taxes while he was mayor of Randolph, while saying, "Conservative Steve Lonegan is just too extreme for New Jersey."
It criticizes Lonegan for supporting cuts to government programs and eliminating support for Planned Parenthood.
But those positions may actually appeal to some conservatives, said a news release from the Independence Hall Tea Party, a Philadelphia-area group that is supporting MacArthur. The group called Patriot Majority's mailer "insidious."
Varoga, Patriot Majority's president, said that both Lonegan and MacArthur "would push a dangerous agenda that would harm middle-class families" and that the ads and mailers "are just the beginning" of its work in the district.
"Both are out of touch, both are dangerous, and both are unqualified," he wrote to The Inquirer in an e-mail.
The ads, though, may have arrived too late in a race that has already seen weeks of brutal attacks, said Patrick Murray, director of the Monmouth University Polling Institute.
"Lonegan and MacArthur are already making so much noise," Murray said, "that I'm not sure that this is going to do anything else."
Sarah Palin endorses N.J.'s Lonegan
WASHINGTON - Sarah Palin has endorsed Steve Lonegan in a heated South Jersey Republican congressional primary.
"Steve is the type of conservative leader we need," Palin wrote Tuesday on her Facebook page. "He believes in the free-market principles this country was founded on because he has seen first-hand how they can lead to success. He will be a dedicated fighter for lower taxes, balanced budgets, and lessening the burdens of regulation on small businesses."
In backing Lonegan, the former GOP vice presidential candidate added her name to a fierce Republican fight playing out in a moderate district with an open seat. Palin also endorsed Lonegan last year in his unsuccessful U.S. Senate campaign against Democrat Cory Booker.
Lonegan, backed by tea party groups, has cast himself as the true conservative in a race against Tom MacArthur, the pick of the local GOP establishment. MacArthur has been endorsed by the current congressman, Republican Jon Runyan, who is not seeking reelection.
The primary is Tuesday. - Jonathan Tamari