Matthew Yglesias asks a question about the American government's willingness to pressure Israel into ceasing settlements in Palestinian territory:
Unfortunately for us, we’re not in one of those periods of time when Israel has a government that’s probably actually not that sympathetic to the settlers but faces domestic political difficulties in cracking down on them. If that were the case, then strong words from the United States might be enough to force change in Israeli policy. But the current government is a coalition between the right and the far-right, and gives every indication of being extremely committed to settlement expansion. This, naturally, raises the question of what American policymakers are prepared to actually do about the fact that the world’s largest recipient of American aid seems to have so little interest in our perspective on crucial regional issues.
"Our perspective" is in fact a reference to Yglesias' perspective, which happens to be roughly in line with Obama's perspective. But it is not necessarily the perspective of the public at large, who tend to side with the Israeli government come hell or high-water. Politicians want to stay in office, and the best way to do that is to get the public on your side. In this case, that means taking a hard-line approach against the Palestinians:
[T]he thrust of US policy in the region derives almost entirely from domestic politics, and especially the activities of the ‘Israel Lobby’. Other special-interest groups have managed to skew foreign policy, but no lobby has managed to divert it as far from what the national interest would suggest, while simultaneously convincing Americans that US interests and those of the other country – in this case, Israel – are essentially identical.
Now, I don't entirely agree with the 'Israel Lobby' argument advanced by Mearsheimer and Walt, but the broader point is impossible to deny: the broad public sides with Israel over the Palestinians for a variety of reasons. This is evident in both political parties and in every national election. Indeed, last week 76 U.S. Senators sent a letter to Obama urging him to "support Israel" without conditions but to demand a host of concessions from Palestine before affirming its right to a state. (Interestingly, the Jerusalem Post article linked above omits the senators' affirmation of the Palestinians' right to a state if they achieve certain pre-conditions; this AFP story keeps the relevant passage in. The letter itself is here [pdf].) This is actually a very different line than the one Obama is taking -- a much harder line towards Palestine -- which shows that even a very popular president will have difficulty galvanizing Congressional support for any policy that is even remotely critical of Israel.
The lesson is that legislators respond to incentives just like anyone else, and the incentives are all aligned in such a way as to practically guarantee universal support for Israel in the Congress, because that is what the electorate wishes to see. So the Congressional movement that Yglesias wishes to see is very unlikely to actually happen.