LINCOLNSHIRE, Ill. (AP) — After fueling months of fights in Washington, President Barack Obama’s nuclear deal with Iran is now popping up in an unusual place: a Democratic primary north of Chicago, splitting party leaders’ loyalties and making Republicans giddy about a potentially weakened opponent in one of 2016’s most competitive U.S. House races.

U.S. Sen. Dick Durbin of Illinois, the minority whip who had the monumental job of securing Democratic support for Obama’s plan, is backing suburban mayor Nancy Rotering over former U.S. Rep. Brad Schneider in the 10th Congressional district primary, largely because she expressed support for the pact and Schneider initially opposed it.

A one-time White House counsel and prominent Democrat who held the seat in the 1970s, Abner Mikva, also abandoned Schneider for Rotering, writing in an open letter that he was disappointed in Schneider for “opposing your president and your party.”

Schneider, who held the seat for one term before losing to Republican U.S. Rep. Bob Dold in 2014, has endorsements from Democratic House Leader Nancy Pelosi, other current House members and the Democratic Congressional Campaign Committee. He also has a fundraising advantage.

But it’s unclear how much sway the Iran deal or big-name endorsements might have when voters go to the polls next month.

Elliott Hartstein, a voter attending a recent primary debate, said the 10th is “a pretty independent-minded district,” and Durbin’s role in the deal isn’t lost on people.

“I wouldn’t say Brad is being punished,” said Hartstein, a former mayor from the suburb of Buffalo Grove who’s backing Schneider. “I’d say Nancy’s being rewarded for basically supporting the president on the issue.”

The accord negotiated with Iran and five world powers aims to curb Iran’s nuclear program in exchange for billions in relief from economic sanctions. Dold has called the agreement “historically bad” because he says it will endanger Israel and the United States.

Buffalo Grove resident Dan Wiczer said the Iran deal isn’t a big issue for him. After seeing Democrats lose in previous general elections, he said he’s more concerned about who will be strongest against Dold in November.

“I give him a lot of courage for wanting to get back in there,” Wiczer said of Schneider returning to the campaign trail after his loss to Dold. “Time will tell.”

Almost immediately after Durbin’s fundraising email endorsed Rotering earlier this month, the National Republican Congressional Committee pounced, saying Democrats would be forced to “waste precious resources.”

“Democrats’ worst fears about an expensive and bloody primary in IL-10 are coming true,” NRCC spokesman Zach Hunter said.

In 2014, the GOP spent close to $7 million nationally to win back the seat, which the party had held for decades before Schneider won it in the first election under new Democrat-drawn maps. Dold’s campaign spent millions on TV ads that didn’t mention he was a Republican.

Schneider expects Democratic turnout this year will be better because there’s a presidential race, and believes the 2014 loss was due to a unique circumstance: Dold’s district is home to Gov. Bruce Rauner, the GOP businessman who unseated an unpopular Democrat. (Since then, the state has been mired in a record budget impasse that’s hurt social services and higher education.)

Rotering counters she’s the strongest candidate not just to take on Dold, but also to hold on to the seat in 2018. She says she’s shown “courageous leadership” by passing an assault weapons ban that was upheld by the U.S. Supreme Court and ripped Schneider for having “stood with Republicans” on the Iran deal.

She says the endorsements have given her campaign “strong momentum.”

The district has a large number of Jewish voters who may be more inclined toward Schneider because of his initial stance.

But now that the deal is in place, Schneider says he supports it “100 percent” and disagrees with GOP attempts to undo it. He said he read the deal six times and consulted multiple experts before concluding he couldn’t support it — a decision he said represented “the values of 10th District.”

He declined to comment on Durbin, Mikva and others backing his rival, saying he prefers to focus on his supporters.

“We both have our endorsements,” Schneider said. “I look at the folks who’ve endorsed me, who know my work, who’ve been with me, who believe in me and I feel that their support as a reflection of all that I have done will carry the day.”