By signing - under intense pressure from the Quartet - the post-disengagement Rafah agreement on November 15 with the Palestinian Authority, Israel committed itself not only to an international crossing on the Gaza-Egypt border, but to facilitating the movement of goods and people between the Palestinian territories. Specifically, Jerusalem promised that by December 15 it would allow bus convoys to transit Gaza and the West Bank. This is not the first time Israel has promised such "safe passage" to the PA. And it's not the first time the PA has made it impossible to implement the arrangement. Sure enough, Prime Minister Ariel Sharon is having second thoughts about the Thursday deadline - and for good reason. The daily prospect of some 1,800 Palestinians traversing between Gaza and the West Bank is worrisome in the context of the grim security situation and Israel's sense that the PA is not living up to the spirit of Rafah. Israel entered into the Rafah agreement with trepidation. But Washington's arm-twisting convinced Jerusalem that cameras and computer data streams would give Israeli security personnel capability to monitor what was happening at the Gaza-Sinai crossing. While the issue is disputed, Israel is convinced that the PA is foot-dragging by not providing the promised real-time flow, and that members of al-Qaida and other Islamist terror groups have been allowed to enter Gaza. The agreement also requires the PA to prevent the movement of weapons and explosives into Gaza. Yet large amounts of these have flowed in from Sinai, at least before the crossing was formally opened. On Saturday, the IDF uncovered a tunnel near the northern Strip apparently intended for a terrorist infiltration. On Friday a navy patrol boat intercepted the third infiltration attempt by sea, in just 10 days, from Egypt to Gaza. Part of the problem is the agreement itself - which does not actually require the PA to stop any terrorist just because Israel insists it do so. Then there is the overall environment. Can Israel abide by a paradoxical situation in which bus convoys of Palestinians traverse the country even as Palestinian missiles are being launched from Gaza, or as Palestinian attackers stab soldiers at checkpoints outside Jerusalem, or as suicide bombers slaughter shoppers lining up to enter a Netanya mall? Sharon told US envoy David Welch that if the Palestinians persisted in their violent ways, Israel would not permit the bus convoys and would even cease tariff cooperation at the Karni and Erez crossings, forcing the PA to pay for goods shipped via Israel. The US is having none of this. Having pressured Israel into a bad agreement in the first place, Washington now insists Jerusalem stick to it. It says Jerusalem is exaggerating Palestinian non-compliance; that the video and data issues are merely technical and anyway on the way to being solved. The backdrop to the bus convoy issue is the Quartet's creditable desire to improve the Palestinian economy. The thinking of the US, UN, EU and Russia is that popular frustration, and with it the appeal of Islamist terrorism, could be reduced by improving the lives of ordinary Palestinians. The World Bank complains that Israel's repeated closures have made it difficult for Palestinians to do business among themselves and with the outside world. The Bank argues that the Palestinian economy has not bounced back to its 1999 pre-intifada levels, and blames Israel. (In fact, according to its own data prepared in advance of a donors' conference set for London in the coming days, unemployment in the Palestinian areas is down, to 22 percent in 2005, the gross national product is up and average income rose in 2005 by some 12%.) But the Bank's complaint is misdirected. Had the PA fulfilled its road map obligations and dismantled the terrorist infrastructure, the Palestinian economy and population would not be hampered by closures. Like the security fence and checkpoints, closures are self-inflicted by Palestinian violence. Clearly, the Rafah agreement alone will not stop terrorists from entering Gaza. Israel is depending on its own and European moral suasion to do that. But the Palestinians must understand that the full implementation of the Rafah deal cannot occur in a vacuum, and the US ought to appreciate this, too. Convoys and Kassams cannot flow at the same time.