In most places in the world, conventional wisdom says that everything changed on Sept. 11. In the Middle East, where irrationality is the norm, nothing has – Israelis and Palestinians continue their horrifying cycle of attack and revenge, as if something that has failed a thousand times will somehow work on the thousand and first.

In a horrifyingly banal way, the attacks this weekend in Jerusalem and Haifa were like those that came before. Innocents were deliberately targeted, 26 were killed and hundreds injured. Credit for the atrocity was claimed by the Palestinian extremist group Hamas. Palestinian Authority leader Yasser Arafat promised a crackdown and arrests. Israel threatened retaliation against the Palestinian Authority.

Yet there are differences. Since the attacks here, civilized nations have come to realize that terrorism is not a localized eruption of resentment, but a concerted and well-funded conspiracy against humanity. The weekend attacks confirmed a grisly pattern – every time an effort is made to advance peace in the region, terrorists strike to derail the process – and a pathetic truth – the terrorists are not just at war with Israel, but with Mr. Arafat and the very concept of Israeli-Palestinian coexistence as well.

The attacks also made clear that a goal of Hamas, the Islamic Jihad and other terrorist groups is to keep the United States out of the region – they came just as U.S. envoy Anthony Zinni arrived to promote a cease-fire plan that called for a crackdown on extremists. The obvious intent is to convince the Bush administration that its first substantive effort to help resolve the conflict should be abandoned as a lost cause.

The Palestinian Authority may have responded to the attacks as usual, with statements of condemnation and a few arrests, but Israel’s threat to dismantle the Palestinian Authority would push events to a new level of irrationality. Israel’s pointless response Monday – destroying two Palestinian Authority helicopters that could be used by security forces to combat the terrorist groups – was not, it is a hoped, a taste of greater irrationality to come.

It is true that Mr. Arafat’s past actions have had more to do with self-preservation than with peace, but eliminating the Palestinian Authority has nothing whatsoever to do with peace. Though it barely resembles a government, it is the closest thing to governance the Palestinians have and it is the sole remaining reminder that the 1994 Oslo peace accords were ever struck. Rather than dismiss the Palestinian Authority as a front for terrorism, Israel and the United States should regard it as a legitimate government under attack and provide it with the necessary military, financial and intelligence support to fight back.

It may also be true, as Defense Secretary Donald Rumsfeld said Sunday, that Mr. Arafat is “not a particularly strong leader.” He is, however, the only leader the Palestinian Authority with the connections and experience to provide an alternative to extremists. Proving himself a true alternative and genuine leader will require Mr. Arafat to break, unequivocally and forever, with Hamas and Islamic Jihad and to use his 40,000-strong security force to destroy their terrorist networks. This all-out confrontation essentially will be his last stand and he cannot be expected to make it alone.