The great Uri Avnery reaches different conclusions than what I wrote on Obama's dilemma; for those interested in this debate, it is must reading: http://www.avnery-news.co.il/english/index.html
In fact, though, I agree with every word of Avnery's contempt for Obama's UN speech, and by implication nearly all of Obama's statements and policies on the Israeli-Palestinian conflict.
Here's Avnery's crucial argument:
"Being a moral person, he must have felt the urge to vomit. Being a pragmatic person, he knew that he had to do it, if he wanted to be re-elected. In essence, he sold the fundamental national interests of the United States of America for the chance of a second term."
Of course Avnery is right that besides being a moral wrong, U.S. support of Israel endangers our national interests in the Middle East. Hence the dilemma: the "fundamental national interests of the United States"--and for Israel and the Palestinians as well--would be also jeopardized if Obama is replaced by any of the likely Republican presidential nominees, which would probably also result in complete Republican control of Congress.
For these reasons, the dilemma should not be framed in terms of Obama "wanting to be reelected," as if this was merely a selfish personal interest.