There's one major issue that President Barack Obama, his supporters and his critics assiduously have avoided as they battle over the deal designed to prevent Iran from obtaining nuclear weapons: Israel's own nuclear arsenal.
An open secret for decades, the Israeli stockpile is estimated at some 80-100 warheads, though Israel refuses to confirm or deny its existence under a policy of deliberate ambiguity. The arsenal was developed as the ultimate guarantor of the Jewish state's survival against threats from its hostile neighborhood.
Yet as the sides joust over the Iran deal's impact on Israel's security, Obama has been silent on the Israeli arsenal as a potential deterrent against Iranian cheating on the accord. Opponents, led by Israeli Prime Minister Benjamin Netanyahu, haven't touched the issue, either. And it hasn't figured in the public hearings that Congress is holding as part of a 60-day review that will culminate in a Republican-led bid to kill the Iran accord next month.
To some experts, the fierce debate over whether the Iran deal endangers Israel or makes it safer will be incomplete and misleading as long as it skirts the Middle East's only nuclear arms stockpile.
"I refer to it (Israel's arsenal) as the 800-pound gorilla in the room," said Avner Cohen, an Israeli-American academic who's written several ground-breaking histories of the Israeli nuclear program. "In all the discussion about Iran and Israel, one must keep in mind that Israel has been a well-established nuclear weapons state for 40 years. It has a very strong, credible deterrent that Iran doesn't have."
Cohen, an Iran deal supporter, also believes that it's difficult to understand Israeli leaders' fervent opposition to the accord - especially Netanyahu's unprecedented interference in domestic US politics - without understanding that they're worried about maintaining an undeclared nuclear monopoly they've enjoyed for decades.
"Part of the 800-pound gorilla missing in the debate is an indication of Israel's true interest," said Cohen, a professor of nonproliferation studies at the Middlebury Institute of International Studies at Monterey, Calif. "Israel's primary but unstated interest is to keep its own nuclear monopoly, in other words, not to allow anyone else (in the region) to have the bomb, not to allow anyone else to even get close to the bomb. The Israelis are concerned that the nuclear deal with Iran effectively provides Iran certain international legitimacy for being a special nuclear status, and the Israelis dont like it."
"You can't talk about the overall security environment in the Middle East unless you address the reality of Israel's own nuclear status," he said.
Others oppose injecting Israel's arsenal into the debate as an unnecessary distraction.
"I don't think it makes sense to factor it in," said Gary Samore, a deal supporter who served as Obama's first senior arms control adviser and recently resigned as head of an advocacy group that opposes the accord. "Nobody involved in this debate ... is saying that it's OK if Iran gets nukes because Israel can deter their use."
Samore, director of research at Harvard University's Belfer Center for Science and International Affairs, believes the discussion needs to stay focused on the purpose of the deal. "The question is: 'Does this deal prevent Iran from getting nuclear weapons?"' he said. He believes it does.
The White House declined to respond to questions about why the Obama administration hasn't made Israel's nuclear deterrent part of the most contentious US foreign policy debate since the 2003 US-led invasion of Iraq. Questions emailed to the Republican chairmen and the senior Democrats on the Senate and House foreign affairs committees went unanswered.
The silence reflects US adherence to a 1969 arrangement - a senior CIA official concluded a year earlier that Israel was capable of building warheads - in which the United States and Israel agreed that both would keep mum about the Israeli weapons program, which is centered at the Dimona nuclear complex in the Negev Desert.
But it also has become a political taboo - Cohen refers to a "code of political silence" - for most serving and former American officials to publicly discuss the Israeli stockpile, which is the target of a longstanding proposal for a UN-recognized weapons-of-mass-destruction-free zone in the Middle East.
Pushed by Iran, Arab nations and others, the proposal is supported by the Obama administration. But the White House doesn't believe that the current conditions in the region are conducive to proceeding with the plan.
Some experts said that discussing the Israeli arsenal could give credence to assertions by Iran that the threat posed by Israel was the reason it concealed what it claims was a peaceful nuclear program from the UN nuclear watchdog for 18 years, until 2002. Most experts believe the real motivation for the program - and an alleged warhead research effort - was the 1980-88 war with Iraq, in which Iran was hit with chemical weapons.
"It would be a mistake to bring Israel's nuclear capability into the Iran debate. Iranians spoke from time to time about shouldn't it (the deal) bring in Israel? But that was for rhetorical purposes," said Robert Einhorn, a retired veteran US diplomat who was on Obama's Iran negotiating team. "When the negotiations got serious, there was never any mention of that. I took their public comments about Israel's capability to be a kind of smokescreen, a diversion."
Israel's nuclear program began in the 1950s. Public disclosure first came in 1986 from a disgruntled Israeli technician, Mordechai Vanunu, who was jailed for 18 years and is barred from traveling abroad.
Numerous details have since emerged in books, academic research, media reports, occasional comments by US and Israeli officials and declassified US diplomatic and top-secret intelligence reports. These reports include a 1974 Special National Intelligence Estimate that declared, "We believe that Israel already has produced nuclear weapons."
The Israeli program was built with foreign aid, especially from France, which helped Israel build its reactor and a plant at Dimona that separates plutonium from spent fuel. Israel also relied on extensive subterfuge, including deceiving American inspectors who visited Dimona, the alleged theft of bomb-grade uranium from the United States and a suspected clandestine test blast off the South African coast in 1979.
Yet as part of the 1969 arrangement to remain silent about Israel's arsenal, the United States reportedly agreed to stop pushing Israel to join the Non-Proliferation Treaty, the keystone of the global system to halt the spread of nuclear weapons. Israel remains outside the treaty - along with nuclear weapons states India, Pakistan and North Korea - while Iran joined in 1968.
Israel's arsenal "would certainly" comprise warheads for mobile missiles and aircraft-deliverable bombs, according to the Federation of Atomic Scientists.
Israel also has taken delivery of five of six advanced German-made submarines reportedly capable of launching nuclear-tipped cruise missiles, which would significantly boost the Jewish state's ability to deter potential existential threats with devastating retribution.
Those capabilities, some experts said, should be part of the Iran deal debate. That's because they raise the question of whether MAD - the theory of mutually assured destruction that many experts believe averted nuclear war between the United States and the former Soviet Union - would apply to Israel and Iran should Tehran secretly develop warheads.
"Israel lives in a dangerous neighborhood, but Israel is well-equipped to deter any nuclear threat that might come from its neighborhood," said Daryl Kimball, a deal supporter who heads the Arms Control Association, a policy institute. "If the Iranians two of three or four decades from now, or another country in the region, were to develop nuclear weapons, it would be extremely dangerous. Yet Israel would retain a mutually assured destruction capability that could potentially deter such a threat."
Samore disagrees. From Israel's perspective, he said, its arsenal didn't dissuade Iran, Iraq, Libya and Syria from pursuing covert nuclear programs. Israeli warplanes destroyed Iraq's reactor in 1981 and Syria's reactor in 2007. The late Libyan dictator Moammar Gadhafi renounced his nuclear weapons program in 2003.
"The whole point of Israel's nuclear arsenal . . . is to deter threats to the country. Except you have to say that from Israel's standpoint, the pressure for proliferation in the Arab Middle East has been steady," Samore said. "From Israel's standpoint, it's hard to argue that having that extra security blanket worked."
Some experts think that the Israeli arsenal could dissuade Iran from secretly developing a nuclear arsenal in violation of its deal with the United States, Russia, China, France, Britain and Germany.
"It's a legitimate discussion point on whether it (the Israeli arsenal) is a check on Iranian cheating (on the nuclear deal). I think it is," said Peter Huessy, a deal critic and president of Geostrategic Analysis, a national security consultancy. "The Israeli nuclear deterrent has absolutely no bearing on whether Iran should have nukes. Iran should not and Israel's deterrent is its own business."
Cohen takes a different tact, arguing that Israel's stockpile outgrew its original role of being Israel's ultimate security guarantor when the Jewish state's conventional military strength surpassed that of any other country in the region decades ago.
Instead, he contended, Israel now relies on its nuclear arsenal, whether deliberate or not, "as a political way to project power and national determination."
"Nuclear weapons, especially for a right-wing-oriented Israel, is no longer a matter of existential survival. It is a way to project Israel as the most powerful, the unchallenged, the strongest factor in the region that can project a sense of strength, confidence and will," said Cohen. "The rise of Iran questions that."