On his visit to Israel in March 2013, President Barack Obama backed Israel’s right to use force to stop Iran from building a nuclear bomb.

At a joint news conference with Israeli Prime Minister Benjamin Netanyahu, Obama said: “…each country has to make its own decisions when it comes to the awesome decision to engage in any kind of military action, and Israel is differently situated than the United States. And I would not expect that the Prime Minister would make a decision about his country’s security and defer that to any other country…”.

Now, in the wake of the Iran deal, the Obama administration is sending dramatically different signals.On the Today show Friday, Secretary of State Kerry said of a pre-emptive Israeli strike on Iran: “That’d be an enormous mistake, a huge mistake with grave consequences for Israel and for the region, and I don’t think it’s necessary.”

Kerry later tried to deflect concerns that the Iran deal requires world powers to secure Iran’s nuclear facilities, downplaying the chance those clauses could be interpreted as requiring the U.S. to defend Iran against Israel.

Yet faced with a choice between defending Israel and defending the Iran deal, it is become clear that under some circumstances, the Obama administration would choose the latter. That is a radically different position from the one Obama took in public just a short time before formal negotiations began.

True, if Israel were to attack Iran preemptively, it would not be the first time it had done so without U.S. backing. President Ronald Reagan condemned Israel’s attack against Iraq in 1981; George W. Bush said “no” to Israel’s 2007 strike against Syria.

But Obama’s new stance suggests something stronger than mere disapproval.

The Iran deal is President Obama’s most important “legacy” achievement. He sees it as the key to his vision of a “new equilibrium” in the region. In the past, he has “preempted” Israel’s preemptive capacity by leaking Israeli attack plans. He may do worse in future–unless Congress defeats the Iran deal and denies him that mandate.

If the deal holds, Israel may soon face the impossible choice of whether to risk America’s new interests for the sake of its own survival.