The current Iran nuclear talks mark a defining moment for President Biden and the new, less-cozy relationship that is shaping up between Biden and Israel, its longtime leader and its American supporters.

Biden campaigned on a pledge to return to the Iran deal, which was brokered by President Barack Obama over the fierce objections of Israeli Prime Minister Benjamin Netanyahu. But until the talks began this month, it was not clear how either leader would handle their differences of opinion, or what they portended for an alliance already in flux.

An attack on a key Iranian nuclear facility, widely attributed to Israel, has made the simmering disagreement suddenly acute.

That attack, an apparent act of sabotage ahead of the second round of talks that opened Thursday, did not derail the effort. But it may make the question of U.S.-Israeli ties more personal for Biden, since his prestige is tied up in the Iran talks.

Biden hailed the talks Friday, while criticizing Iran’s decision to increase its uranium enrichment in violation of the agreement.

“And so discussions are underway,” Biden said during a news conference. “I think it’s premature to make a judgment as to what the outcome will be, but we’re still talking,” Biden said.

Overall, the new president is signaling that he feels less inclination than his predecessors to showcase a closeness with Israel. Democrats in general have become more skeptical of the Jewish state in recent years, while Israeli leaders have aligned themselves more closely with the GOP — a significant shift in the 73-year relationship between the two countries.

The White House declined to comment for this article.

At the start of a two-day visit to Israel, Defense Secretary Lloyd Austin spoke in a joint statement with Israeli Defense Minister Benny Gantz on April 11. (The Washington Post)

The disruption at the Natanz nuclear facility came as Defense Secretary Lloyd Austin visited Israel on Sunday. If Israel was behind the attack, as analysts believe, then the country apparently timed it not only to sabotage the Iran talks underway in Vienna, but also to send a message to Washington by embarrassing the visiting U.S. defense chief.

“Who knows what went into it, but the optics of Secretary Austin being in Israel the morning of the attack really puts the administration in a difficult position,” said Kaleigh Thomas, a Middle East specialist at the Center for a New American Security (CNAS).

Israel has not commented formally on the attack, which Iran has called “nuclear terrorism” perpetrated by Israel. U.S. officials have denied any involvement while declining to assign blame.

Biden has known Netanyahu for decades, and has not forgotten what he considers previous slights from the Israeli leader, including Netanyahu’s address to Congress arguing against the 2015 Iran nuclear deal. Republicans had invited the hawkish prime minister to speak without consulting Obama or Biden, who was then vice president — a major diplomatic snub.

Although Biden and Netanyahu professed a warm friendship after Biden’s election, the president kept Netanyahu waiting for weeks before granting an official call. The signal was clear: Netanyahu’s open line to the White House under President Donald Trump had closed.

The contrast was striking, because Trump and Netanyahu had exhibited their affinity for each other in unprecedented ways. Trump moved the U.S. Embassy to Jerusalem, for example, which other presidents had resisted doing for decades. He endorsed permanent Israeli control of the disputed Golan Heights, another longtime taboo.

Netanyahu, for his part, featured himself with Trump in campaign posters to bolster his slogan that he was in a “different league” than his rivals. He even sought to name an Israeli settlement “Trump Heights.”

The result has been to align Israel, which has enjoyed bipartisan support as a central U.S. partner since its founding in 1948, more closely with the Republican Party.

At the same time, a growing number of younger figures within the Democratic Party, such as Rep. Rashida Tlaib (D-Mich.), whose parents are Palestinian, have been willing to criticize Israel more strongly.

Biden may draw closer to Israel if Netanyahu is replaced at some point by a more conciliatory, less pugnacious leader. In the meantime, the pivot from the Trump years is evident in moves like Biden’s decision to resume support payments for Palestinians, and in his rhetorical recommitment to the goal of an independent Palestinian state.

More broadly, Biden also seems less caught up in the notion of brokering peace in the Middle East than most presidents, many of whom have taken office finding the idea almost irresistible. He has not made any move to resume negotiations between Israel and the Palestinians, nor suggested that he plans a bold gesture later.

Rather, Biden has downgraded the Middle East as a strategic priority, as his administration seeks to redirect foreign policy muscle to Asia.

Biden, a veteran Democratic politician, is well acquainted with the strength of pro-Israel sentiment, and the lobbies that support it, in the United States. But the administration has not named an official liaison to Jewish groups. Biden has not nominated a U.S. ambassador to Israel, although a prominent Biden donor, Michael Adler, is reported to have sought the post.

Nor does the administration appear to be doing much to address the concerns by some pro-Israel groups about the U.S. resuming talks with Iran.

The American Israel Public Affairs Committee, the largest such group, canceled its annual policy conference this spring because of the coronavirus pandemic. That meant Biden did not have to face a potentially skeptical reception from the conservative-leaning group, nor did he confront the problem of declining an invitation if he chose to do so.

But Biden is also not attending an online conference planned for Sunday and Monday by J Street, a liberal pro-Israel group that is a strong backer of his policies, though Linda Thomas-Greenfield, the ambassador to the United Nations, and Cedric L. Richmond, Biden’s public engagement director, will be speaking at the event.

J Street President Jeremy Ben-Ami said he was not troubled by Biden’s absence. “I still think it’s early days. I think we’re not even at the 100-day mark, and I don’t know that they have all the key players in place,” Ben-Ami said. “So I still give them a bit of a pass as far as outreach.”

Ben-Ami and others said Biden has reason to keep some distance from Netanyahu now. Israel remains politically paralyzed, potentially headed for a fifth election in roughly two years, while Netanyahu himself faces trial on corruption charges.

For his part, Netanyahu knows he is on thinner ice with the United States, Thomas of CNAS said.

“Everyone’s seeing the writing on the wall — there is going to be a shift in the U.S.-Israel relationship,” she said. “I don’t think just because of Biden, but because Israel has gotten more criticism in D.C.,” especially from Democrats during the Trump era, she said.

The dispute over Iran quickly emerged as the biggest flash point for these new dynamics, even before the Natanz attack, but especially since.

Iran announced that it would increase uranium enrichment to 60 percent purity in response to the attack. That level is far above what is tolerated under the nuclear agreement, and it further complicates the task of resurrecting it.

That would be fine with Netanyahu. “Netanyahu is against any agreement with Iran. Any,” said Alon Pinkas, a former senior Israeli diplomat.

Trump quit the agreement in 2018, and began reapplying punitive sanctions to Iran. Iran then began breaking its commitments under the deal, arguing that it was not reaping the promised benefits because of Trump’s actions.

The goal of the current talks is to find a way for the United States and Iran to simultaneously return to the agreement, whose other signatories include China, Russia, France, Britain and Germany.

U.S. and Israeli officials sought to project calm following the Natanz attack, and the incident did not derail either Austin’s visit or a virtual meeting last Tuesday between national security adviser Jake Sullivan and his Israeli counterpart.

“We don’t have any additional speculation to add to the cause or the origin of the attacks over the weekend,” White House press secretary Jen Psaki said Wednesday. “What our focus is on, is on the diplomatic path forward.”

But it is not clear that Iran and the U.S. can navigate back to the agreement. And how that unfolding drama will affect the U.S.-Israel relationship is also uncertain, said a diplomat familiar with Israel’s thinking.

“Their ultimate goal is similar to ours — to prevent Iran from obtaining a nuclear weapon. No argument there,” said the diplomat, who spoke on the condition of anonymity to discuss diplomatic relations. “Now, their intermediate goal is to go back to the deal in order to negotiate a better one, which we strongly disagree with.”

Even if negotiations succeed, Biden will face domestic political hurdles. Congress is expected to weigh in, as it did in 2015. Although Democrats narrowly control both chambers of Congress, a handful of Democratic senators who voted against the initial deal remain in office — including the chairman of the Senate Foreign Relations Committee, Sen. Robert Menendez (D-N.J.).

Twenty-seven of the 50 Senate Democrats have gone on record backing Biden’s effort to rejoin the agreement, formally known as the Joint Comprehensive Plan of Action, or JCPOA. They contend that a deal with Iran, however imperfect, is better than a hostile standoff that allows Iran to amass the components of a nuclear weapon at will.

“We will continue to challenge our colleagues who are critics of the administration’s intention to rejoin the JCPOA to say what the alternative is,” said a Democratic aide, who spoke on the condition of anonymity to discuss sensitive party dynamics. “We have tested the ‘maximum pressure’ strategy for four years.”

Trump called his approach a “maximum pressure campaign,” saying it would force Iran to negotiate a new agreement, on terms better for the United States, that would also address issues beyond the nuclear program.

Democrats dismiss that as wishful thinking, arguing that Iran is now closer to being able to build a bomb than it was when Trump pulled out. Tehran denies it intends to build a weapon.

But as Iran draws closer to amassing sufficient material for a nuclear bomb, the time for the Biden administration to find a diplomatic solution is limited. As the Democratic aide put it, “There’s a clock on this.”