The easy assumption about President Obama's United Nations speech — coming as it did after months of complaints by pro-Israel Jews, and directly on the heels of a special election loss in a heavily Jewish district in New York — is that it was a sort of concession to domestic politics. (See the staunchly pro-Israel David Frum for a sample of this argument.) I think that's wrong.
Obama's position was always going to be the second part of a two-step process. Last Spring, when Obama advocated a negotiated settlement with land swaps based on 1967 borders and right-wing Zionists flipped out, I argued that Obama was establishing the credibility he (and Israel) would badly need when the September vote arrived, and that he was going to take the position he has in fact taken.
Obama's international strategy is pretty much the same thing as Obama's domestic political strategy. The first part involves extending a hand to your adversary and demonstrating your own reasonableness. Assuming they don't take it, the second involves more traditional hardball politics. In this case, Obama is using the method to defend the traditional U.S.-Israel alliance, but it works the same way for advocating Democratic positions on jobs or the deficit or health care. Obama always starts out his strategy alarming his allies.
Of course, the political timing works out conveniently for Obama. He gets to head into the elections having stood up for Israel at the U.N., not having jostled publicly with Netanyahu. Perhaps Obama would be looking for a political solution if this opportunity had not presented itself. But it so happens that there is a coherent diplomatic strategy here that happens to mesh with Obama's reelection needs.