The threat – from both men – was clear. Military action, albeit only as last resort, but a war nonetheless against Iran to keep the Islamic regime from joining the ranks of the nuclear-armed.
If Iran's ruling mullahs rose early Tuesday to watch America's presidential contenders scrap over foreign policy in their final debate, they would have seen both Barack Obama and Mitt Romney delivering the same grim message.
While they sparred over the depth of their devotion to Israel and traded jibes over power projection, on Iran only nuance separated their last-ditch willingness to wage war; a war that would likely need at least weeks of air strikes to devastate Iran's widely-spaced and deeply-buried nuclear sites.
"A nuclear-capable Iran is unacceptable to America," said Mr. Romney. "It presents a threat not only to our friends, but ultimately a threat to us."
The Republican challenger's use of the term "nuclear-capable" suggested his threshold was a little lower, perhaps closer to Israel's red line that Prime Minister Benjamin Netanyahu suggested might be crossed within months if Tehran's centrifuges keep enriching uranium closer to weapons-grade levels.
Mr. Obama said, "as long as I'm president of the United States, Iran will not get a nuclear weapon."
That's perhaps further away, although experts differ as to how much further while Tehran insists it has no military interest in its nuclear program. Still, a weapon requires miniaturization and testing and the crucial capability to deliver a warhead by missile or manned bomber.
The distinction may not matter to key groups of undecided voters in a handful of swing states who will choose two weeks from today which man will be in the Oval Office when and if the time comes for the fateful decision to launch missile and air strikes against Iran.
Still, the Romney red line and the Obama red line aren't quite the same.
And both ducked when asked what they would do if the call came that Israeli warplanes were in the air headed for Iranian targets; the sort of unilateral first-strike that Israel twice previously launched against nuclear sites in Iraq in 1981 and Syria in 2007. Mr. Romney said – likely accurately – that such a call would never come, that a U.S. president would know well in advance of an Israeli attack. Mr. Obama just ignored the hypothetical.
Still, their absolute assurances of backing for Israel may bedevil the vexed problem of dealing with Tehran and its nuclear program as the entire Middle East is wracked by turmoil and change.
"If Israel is attacked, we have their back, not just diplomatically, not just culturally, but militarily," Mr. Romney said.
As did Mr. Obama, who vowed "If Israel is attacked, America will stand with Israel."
That's not the same as being willing to back Israel if it strikes first and the deliberate ambiguity leaves plenty of room for uncertainty and risk.
Mr. Romney accused Mr. Obama of dithering and letting Iran get "four years closer to a nuclear weapon" while the president said U.S.-led sanctions have crippled the Islamic regime.
In Monday's third – and final – presidential debate, the two rivals often offered few differences on policy even as they lambasted the other for failings.
They concurred, for instance, on Syria, saying there will be no repeat of Libya, where U.S. warplanes and cruise missiles launched a major allied air war that tipped the balance against Moammar Gadhafi.
In Syria, both men ruled out U.S. military involvement. Where they differed was on giving arms to Syrian insurgents battling to topple President Bashar al-Assad's brutal regime, despite 30,000 deaths and hundreds of thousands driven from their homes in more than a year of worsening violence.
Mr. Romney accused Mr. Obama of failing to lead and said he would provide arms to the anti-Assad forces. The president admitted events were "heartbreaking" but warned that sending weapons into the Syrian war might backfire: "… that we're not putting arms in the hands of folks who eventually could turn them against us or our allies."