Khaled Abdullah / REUTERS Members of the Republican Guards stand in line at a barricade blocking protesters supporting deposed Egyptian President Mohamed Mursi near a Republican Guards headquarters in Cairo July 9, 2013.

As Washington debates whether to cut off America’s $1.5 billion in annual assistance to Egypt, few countries are watching with more interest than Israel. On Monday the Tel Aviv newspaper Haaretz reported that Israeli officials have urged President Barack Obama to keep subsidizing Cairo despite the legal prohibition on U.S. aid to governments installed by military coup. That’s no surprise: “Israel has always been a very strong proponent of the assistance program,” says Frank Wisner, a former U.S. ambassador to Cairo. “It is in Israel’s interest that the U.S. maintain a very strong relationship with Egypt.” But understanding why that is goes to the heart of America’s relationship with Egypt–and why Obama is so reluctant to disrupt it.

Israel is the prime reason why Egypt has for nearly 25 years been the second-largest recipient of U.S. foreign aid. (The top recipient is–you guessed it–Israel.) American largesse began flowing to Cairo in 1979, after Egypt’s then-president, Anwar Sadat, signed the September 1978 Camp David accords establishing peace between Egypt and Israel. That was a remarkable development, considering the two nations had conducted four armed conflicts in the first 25 years of Israel’s existence, and given the deep hostility within Egypt towards the Jewish state.

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With his country economically stagnant, however, Sadat saw the accords as a new hope for Egypt. They would reclaim the Sinai desert lost to Israel in 1967; end a constant state of war on its border; move Cairo from Moscow’s orbit into Washington’s; and help to advance the Palestinian cause. But Sadat’s people didn’t see the final product that way: “Peace with Israel had become a betrayal,” writes Steven A. Cook of the Council on Foreign Relations in his 2011 book The Struggle for Egypt. Indeed, signing the American-brokered peace deal would cost Sadat his life when an Islamist army soldier gunned him down as he reviewed a military parade on October 6, 1981.

But the peace deal survived the murder of the man who sealed it. And so did the generous American aid that soon began as a result of the accords (in what Cook, via email, calls “an informal payoff”). That aid has actually grown less generous, however. Since 1998, Congress has cut non-military assistance to Egypt from $815 million to $250 million. Meanwhile the $1.3 billion in military funds that Washington grants Cairo has not increased in 30 years; its inflation-adjusted value has dropped by more than half. That still allows Egypt to purchase state of the art equipment, largely consisting of M-1 Abrams tanks and F-16 fighter jets. But thanks to a lack of trained personnel, not to mention peace on its borders, “most of the time these tanks and aircraft are just gathering dust,” says Tarek Radwan of the Rafik Hariri Center for the Middle East at the Atlantic Council. (On Wednesday Reuters reported that the U.S. will allow the delivery to Egypt of four already-purchased F-16s.)

More important, then, is the symbolic goodwill and very tangible direct relations with the Egyptian army that money purchases. That’s in the interest of Washington officials who want influence within the Arab world’s most populous country. And it’s most welcome in Israel, which, far from fearing Egypt’s armed forces, sees them as a buffer against extremists who might prefer a return to hostilities. “Israel sees the Egyptian military as a pro-peace lobby inside the Egyptian political system,” says David Makovsky, a senior fellow at the Washington Institute for Near East Policy.

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The peace deal, and Washington’s influence over Egypt, helps Israel in other ways. Egyptian forces secure Egypt’s border with Israeli in the Sinai, as well as the nearby border with Gaza, likely preventing terrorist attacks on Israel from the area. Makovsky also notes Egypt’s influence with Palestinian leaders. While its ousted president, Mohamed Morsi, tilted towards the radicals of Hamas, Egypt’s military and its political allies are closer to the moderate Palestinian president, Mahmoud Abbas, who was quick to “congratulate the Egyptian leadership in this transitional phase of its history.”

No one thinks a cutoff of American aid would lead to another war between Israel and Egypt. Anti-Semitism is rampant in Egypt, and Israeli diplomats live and work under tight security. But a pragmatic peace endures: Makovsky recalls being in Cairo with then-Israeli Prime Minister Yitzhak Rabin and hearing Sadat’s successor, Hosni Mubarak, declare that war with Israel knocks out a generation of economic development for Egypt. “The U.S. and Israel don’t want wars,” Makovsky says. “Egypt doesn’t want war. Everybody’s happy. There’s no incentive for anybody to change that.” Even Morsi, who once urged Egyptians “to nurse our children and grandchildren on hatred towards those Zionists and Jews, and all those who support them,” didn’t try to end peace with Israel.

Even so, Israel would prefer not to tinker with a formula that has served its interests quite well for a generation–particularly when it has growing threats from Syria and Iran to worry about. Moreover, as Jeffrey Goldberg notes , Pakistan offers a cautionary lesson in what can become of a foreign military’s officer corps when U.S. aid is suddenly withdrawn.