Last week the US Supreme Court ruled a law passed by Congress 13 years ago was unconstitutional. This enactment sought to give US parents of children born in Jerusalem the right to obtain for their offspring passports indicating the children had been born in Israel. But on June 8, the Justices of the Supreme Court "struck down" this law. In so doing the Court rejected the contention of Ari Zivotofsky, an American, that although his son, Menachem, had been born in Jerusalem, Menachem's US passport could not give the place of birth as "Jerusalem, Israel", but must restrict itself to the single word "Jerusalem".

The Palestinian leadership lost no time in seizing upon this ruling as a blow against the Jewish state. Saeb Erekat, the Palestinian Authority's chief negotiator, welcomed the decision. Jerusalem, he declared, "is an occupied territory", and the Supreme Court had sent "a clear message to the Israeli government that its decisions and measures in occupying and annexing Jerusalem are illegal and void and that it should immediately stop these measures because it's a clear violation of the international law". He added, for good measure, that the ruling meant that Israel's "policies of colonization are null and void".

But while it's certainly the case that the Court's decision reverses the long-term and hitherto unimpeded efforts of Congress to use American law to underpin Jerusalem's status as an integral, undisputed part of Israel (whether or not it is regarded also Israel's capital), the devil is in the detail. And had Mr Erekat and his supporters stopped to examine and contemplate this detail they might not have given the Supreme Court's decision such an uncritically euphoric reception.

In the first place, the Supreme Court made no ruling on whether Jerusalem was in fact part of Israel. That was not their business. The justices based their determination exclusively on their construction of the American constitution, which - they said - reserves the right to determine the foreign policy of the US exclusively to the executive branch of government - that is, to the President and the Secretary of State. It was in those terms, therefore, that they ruled as unconstitutional that part of the 2002 Foreign Relations Authorisation Act that sought to bind the discretion of the executive when parents demanded that the word "Israel" appear next to "Jerusalem" on the passports of Jerusalem-born children.

In signing that law, President George W Bush observed that the clause in question interfered "impermissibly with the president's constitutional authority to conduct the nation's foreign affairs". The Supreme Court has now supported this contention. But it has not ruled on the constitutionality of an earlier law, the Jerusalem Embassy Act of 1995, which binds the US to recognise Jerusalem undivided as Israel's capital. President Clinton disapproved of this legislation, and refused to implement it. But he also declined to veto it, and it became law by default.

In urging the Supreme Court to rule against the constitutionality of the passport legislation, the Obama administration argued that to be compelled to put the word "Israel" after the word "Jerusalem" would tie the hands of the executive in the context of peacemaking in the Middle East, because it would be tantamount to a pre-determination of the core issue of the final status of Jerusalem within any peacemaking framework. That's certainly true. But, if that is the case, what's equally true is that President Obama cannot in all conscience now support any initiative - say, at the United Nations - that seeks to endorse the recognition of a Palestinian state incorporating any part of Jerusalem within its borders.

It's common knowledge that France, a permanent member of the UN Security Council, is planning to table a resolution calling for the recognition of a Palestinian state encompassing part of Jerusalem as its capital. If Obama were to support this initiative - as he is rumoured to be considering - this would surely run counter to the argument he successfully deployed before the Supreme Court: that the final status of Jerusalem must await the outcome of bilateral negotiations between Israel and the Palestinian Authority, in which negotiations it is - apparently - imperative for the US to maintain the strictest of neutralities.