This afternoon, President Obama praised Egyptian demonstrators whose 18-day protests resulted in the ouster of President Hosni Mubarak. Hearkening back to the legacy of Martin Luther King Jr., Obama said Egyptians had "bent the arc of history toward justice once more." Israeli leaders, however, are decidedly less enthusiastic.

"They're worried," Slate's Brian Palmer writes. Mubarak's Egypt had been one of Israel's closest Middle Eastern allies. It was early to recognize Israel's legitimacy. It worked towards blocking arms into Palestine and it respected Israel's embargo of the Gaza Strip. So what happens now? Israel's policies are deeply unpopular in many quarters of Egyptian society. Will a more representative Egyptian government imperil Israel? Will it pressure the Israelis to forge agreements with its neighbors? Here are some of the potential outcomes of Mubarak's historic fall.

Further Isolation  The Wall Street Journal quotes former Israeli officials worrying about a "wider transformation" in the Middle East leading to fewer partners in the region. "We have a tough period ahead of us," said Zvi Mazel, a former Israeli ambassador in Egypt. "Iran and Turkey will consolidate positions against us. Forget about the former Egypt. Now it's a completely new reality, and it won't be easy." Some Israelis also fear that unrest could strike in Jordan, which Israel has a peace deal with.

Some Agreements with Egypt Will Dissolve, Some Will Not  Amjad Atallah at the New America Foundation lays out the most vulnerable ones:

Any new Egyptian government [will] respect the Camp David Accords as it afforded a real benefit to Egypt – the return to Egypt of the Sinai Peninsula from Israeli occupation. However, it is equally likely that no representative Egyptian leader will be able to continue the siege of the Gaza Strip, support efforts to keep the Palestinians divided or tolerate another Israeli attack on Gaza.
This Will Blot Netanyahu's Legacy Shibley Telhami, a senior fellow at the Brookings Institution, thinks this will become a major issue in Israeli politics:
Benjamin Netanyahu will likely be seen by future Israelis as the prime minister who lost Egypt. Egypt has been such an anchor of the Israeli approach to regional security and peace negotiations since the Camp David Accords in 1978 that its role has been taken for granted — in part because successive Israeli governments have assumed that the Egyptian-American relationship and the U.S. foreign aid to Egypt, as well as the Mubarak regime’s own interests, guaranteed Israeli-Egyptian relations would be stable no matter what happened on other fronts.
Israel Could Become a Stronger Partner for Peace  Slate's Brian Palmer notes that Israel has faced similar geopolitical shifts like this before. It could very well encourage them to strike peace deals with other Middle East regimes:
Israel forged its peace with Egypt around the time that its former ally, the Shah of Iran, was deposed. It's likely the instability in Egypt will motivate Netanyahu to strengthen ties with Jordan or even Syria, which might be looking to improve relations with the U.S.