JERUSALEM — It took President Obama two days to call Prime Minister Benjamin Netanyahu of Israel after his March 17 electoral victory, and any congratulations were couched in an excoriation of Mr. Netanyahu’s hawkish and divisive campaign rhetoric.

It took Mr. Obama about two hours to call Mr. Netanyahu after Thursday’s announcement of a framework agreement to curb Iran’s nuclear program, and this time it was the Israeli leader who lectured the American that the emerging deal “would threaten the survival” of his state. The White House account of the call was conciliatory: The president promised to increase security consultations and cooperation with Israel to “remain vigilant in countering Iran’s threats.”

The relationship between the two leaders, and their nations, has always been asymmetrical: The United States is the world’s sole superpower, Israel a small country in a volatile neighborhood. But while Mr. Obama’s promised reassessment of Washington’s longstanding protection of Israel in the United Nations flexes that larger muscle, Mr. Netanyahu is now in a powerful position to undermine the Iran nuclear deal, his counterpart’s signature foreign policy initiative.

How fiercely Israel fights the deal, particularly in Congress, could have broad implications for the strained alliance and the Middle East peace process.