(CNN) - Former Democratic New York Mayor Ed Koch said Tuesday he wants Republicans to take the district formerly represented by Rep. Anthony Weiner–a seat held by Democrats for decades.
Expressing outrage over President Barack Obama's views on Israel, Koch warned in an interview that the Sept. 13 special election to replace Weiner could become a bellwether on the president's recent calls for Israel to return to its 1967 borders with land swaps.
New York's 9th congressional district, which covers parts of Brooklyn and Queens, is one of the most Jewish districts in the country.
Koch compared the race to the 2010 Massachusetts senate race when Republican Scott Brown won the longtime Democratic seat vacated by Sen. Ted Kennedy after his death in 2009. The GOP victory was widely considered a referendum on the senate's Democratic supermajority in Congress.
"That election changed Obama," Koch said. "Today he's far more centrist because of it."
Koch believes the same effect would happen to the president's policy on Israel should the heavily Democratic district in New York elect a Republican to the House.
"It will be another political shot heard around the nation," Koch wrote in an email Monday to Republicans, announcing his view.
The three-term mayor insisted the president would be paying close attention to the outcome of the special election, which recently got underway when local Republican and Democratic parties chose their nominees.
While the Democratic pick, David Weprin, is an observant Jew and a New York assemblyman with a storied family in Queens County politics, the nominee has drawn criticism from the local Jewish community on voting for New York's recently-passed same sex marriage law.
But when it comes to foreign policy, Democratic campaign sources point to Weprin's strong pro-Israeli stance. And, if elected, Weprin would be the only Orthodox Jew in the House of Representatives.
"Nobody is a stronger supporter of Israel than David Weprin," said campaign spokesman Evan Stavisky. "Not only will David Weprin fight for Israel, he'll also fight to protect the Jewish community in Queens and Brooklyn from House Republicans' devastating cuts to Medicare, Medicaid and Social Security."
Koch told CNN he has no problem with Weprin, whose brother, Mark, worked in Koch's administration. But the former mayor says the special election in NY-9 presents an opportunity to send a message to the White House.
"This issue is bigger than David Weprin," Koch said. "Of course he's a supporter of Israel, but his election is not going to change Obama."
After Obama's Mideast speech in May, media reports cited slipping support for the president among the Jewish community. But a recent Gallup poll showed a majority of Jewish Americans still approve of Obama at 60 percent.
Republicans in the 9th district hope their candidate, businessman Bob Turner, will make strides in the race by maintaining the party line on Israel. Turner challenged Weiner for the seat in November and lost with 40 percent of the vote, a higher-than-normal Republican finish in the district.
Koch has been known in the past to cross party lines and endorse Republicans. In 2004, he backed President George W. Bush's re-election bid. He also supported Rudy Giuliani in the Republican's first run for New York Mayor.
But Koch's recent comments aren't an endorsement for Turner. The Republican candidate would have to campaign against spending cuts in Medicare, Medicaid and Social Security–an unlikely scenario–to get the former mayor's full support, Koch said.
When asked who Koch would endorse if Turner, a staunch conservative, doesn't switch his position on entitlements, Koch said he would withhold comment for now.
"But I probably won't endorse anyone, since it would go Democrat, anyway," Koch said.
However, in his email to Republicans Monday, the Democrat closed his message hoping voters would make "history" by electing a Republican.
"They can consign themselves to oblivion or be remembered in the history books," Koch wrote.