There are no other guarantors available. Israeli Prime Minister Benjamin Netanyahu went to Moscow, clearly trying to get the Russians to block the agreement. He failed. But even if he had succeeded, he would have alienated the United States, and would have gotten instead a patron incapable of supplying the type of equipment Israel might need when Israel might need it. The fact is that neither the Saudis nor the Israelis have a potential patron other than the United States.
U.S. Regional Policy
The United States is not abandoning either Israel or Saudi Arabia. A regional policy based solely on the Iranians would be irrational. What the United States wants to do is retain its relationship with Israel and Saudi Arabia, but on modified terms. The modification is that U.S. support will come in the context of a balance of power, particularly between Iran and Saudi Arabia. While the United States is prepared to support the Saudis in that context, it will not simply support them absolutely. The Saudis and Israelis will have to live with things that they have not had to live with before -- namely, an American concern for a reasonably strong and stable Iran regardless of its ideology.
The American strategy is built on experience in Iraq and Afghanistan. Washington has learned that it has interests in the region, but that the direct use of American force cannot achieve those goals, partly because imposing solutions takes more force than the United States has and partly because the more force it uses, the more resistance it generates. Therefore, the United States needs a means of minimizing its interests, and pursuing those it has without direct force.
With its interests being limited, the United States' strategy is a balance of power. The most natural balance of power is Sunni versus Shia, the Arabs against the Iranians. The goal is not war, but sufficient force on each side to paralyze the other. In that sense, a stable Iran and a more self-reliant Saudi Arabia are needed. Saudi Arabia is not abandoned, but nor is it the sole interest of the United States.
In the same sense, the United States is committed to the survival of Israel. If Iranian nuclear weapons are prevented, the United States has fulfilled that commitment, since there are no current threats that could conceivably threaten Israeli survival. Israel's other interests, such as building settlements in the West Bank, do not require American support. If the United States determines that they do not serve American interests (for example, because they radicalize the region and threaten the survival of Jordan), then the United States will force Israel to abandon the settlements by threatening to change its relationship with Israel. If the settlements do not threaten American interests, then they are Israel's problem.
Israel has outgrown its dependence on the United States. It is not clear that Israel is comfortable with its own maturation, but the United States has entered a new period where what America wants is a mature Israel that can pursue its interests without recourse to the United States. And if Israel finds it cannot have what it wants without American support, Israel may not get that support, unless Israel's survival is at stake.
In the same sense, the perpetual Saudi inability to create an armed force capable of effectively defending itself has led the United States to send troops on occasion -- and contractors always -- to deal with the problem. Under the new strategy, the expectation is that Saudi soldiers will fight Saudi Arabia's wars -- with American assistance as needed, but not as an alternative force.
With this opening to Iran, the United States will no longer be bound by its Israeli and Saudi relationships. They will not be abandoned, but the United States has broader interests than those relationships, and at the same time few interests that rise to the level of prompting it to directly involve U.S. troops. The Saudis will have to exert themselves to balance the Iranians, and Israel will have to wend its way in a world where it has no strategic threats, but only strategic problems, like everyone else has. It is not a world in which Israeli or Saudi rigidity can sustain itself.
