Because he's a right-wing extremist on Israel, and therefore opposes President Obama's moderate views on Israel and the ongoing Israeli-Palestinian conflict, former New York City Mayor Ed Koch wants a Republican to replace Anthony Weiner in New York's 9th Congressional District, a heavily Jewish district in Brooklyn and Queens. A Republican win, he thinks, would "be another political shot heard around the nation" and make Obama more centrist (i.e., more pro-Israel in a way he approves). No matter that the Democratic candidate, David Weprin is an Orthodox Jew with conservative views on Israel. For Koch, it's all about sending a message to the White House.
All of which is complete nonsense. Koch won't be happy unless Obama, or any president, embraces Likudnik extremism. Sensible moderation isn't enough. But, then, this election should be (and will be) about more than just Israel (and Obama's Israel policy), even in a heavily Jewish district. Other issues are just as much on the minds of voters, if not much more so, and it's silly to think that the vote should be a referendum of sorts on Obama's views on Israel without any regard for the views of the candidates themselves or of the various other concerns of voters. Koch would seem to have a one-track mind. The voters in NY-9 surely have other priorities.