The democrats will face mid-term elections next year, and Israel needs American support at the UN. Substantial losses in the House and Senate may derail Obama's ability to help the US economy they way he wants which may cause him problems in the election of 2012. Israel is, obviously, under extreme pressure in the UN, with Iran, with the changes cause by Abbas' resignation, and with growing militancy by many Palestinians. Without some compromises, both could lose.
Knesset passes 'Norwegian Law' allowing ministers to resign their seats, remain in cabinet (Haaretz)
from the article: Does Obama delay in scheduling Netanyahu meet point to crisis?