During the 2012 campaign, President Obama had a simple message for his would-be Republican rivals and their tough talk on Iran. "If some of these folks think that it's time to launch a war, they should say so," Obama warned, "And they should explain to the American people exactly why they would do that and what the consequences would be."

Three years later, conservatives like Joshua Muravchik are taking Obama's challenge, or at least, the first part of it. In the sequel to his 2006 Los Angeles Times op-ed titled simply, "Bomb Iran," Muravchik on Friday took to the pages of the Washington Post to declare, "War with Iran is probably our best option." But if he is dangerously glib about what it will take to completely neutralize the Iranian nuclear infrastructure ("we can strike as often as necessary") and the real costs in doing so ("we might absorb some strikes"), he is silent about what the world looks like the day after the United States launches its campaign for what he really desires, regime change in Tehran.
Fortunately, leaders of the national security establishments in both Israel and the U.S. have spoken clearly on what war with Iran will look like and what it will cost. Short of a total invasion and occupation of that nation of 75 million people, the deployment of Iranian nuclear weapons can only be delayed, not halted, by military action. And the resulting carnage and chaos throughout the Middle East would make the U.S. conflicts in Afghanistan and Iraq seems like picnics in comparison.
At the core of the dispute between President Obama and Prime Minister Netanyahu are their different "red lines" with Iran. Throughout, the President has said he will not allow Tehran to actually build a nuclear weapon. As he put it during his 2013 visit to Israel:

I've made the position of the United States of America clear: Iran must not get a nuclear weapon. This is not a danger that can be contained, and as President, I've said all options are on the table for achieving our objectives. America will do what we must to prevent a nuclear-armed Iran.

But for Netanyahu, as Mitt Romney explained during the 2012 campaign, the red line is drawn far short of possession:

"With regards to the red line, I would imagine Prime Minister Netanyahu is referring to a red line over which if Iran crossed it would take military action. And for me, it is unacceptable or Iran to have the capability of building a nuclear weapon, which they could use in the Middle East or elsewhere. So for me, the red line is nuclear capability. We do not want them to have the capacity of building a bomb that threatens ourselves, our friends, and the world."

That's why Israel for five years has warned the United States it would not hesitate to act alone--and without advance warning to Washington--against Tehran's nuclear targets.
While it's true the United States received no advance warning about the Israeli bombing of Iraq's Osirak nuclear reactor in 1981 or suspected Syrian facilities in 2007, the Iranian scenario is altogether different. Neither Saddam Hussein (then an American ally) nor Bashar Al-Assad posed a serious threat of military retaliation to the one-off Israeli strikes. Crippling Tehran's nuclear capability would require a sustained military campaign that, short of total invasion and occupation, would only temporarily delay the Iranian program. And the danger from an Iranian response is quantitatively and qualitatively of a different magnitude.
At a minimum, thousands of Iranian civilians would die in an American attack against Tehran's nuclear installations. Even if the Israelis alone launch a strike against Iran's nuclear sites, Tehran will almost certainly hit back against U.S. targets in the Straits of Hormuz, in the region, possibly in Europe, and even potentially in the American homeland. And Israel would face certain retaliation from Hezbollah rockets launched from Lebanon and Hamas missiles raining down from Gaza.
That's why it came as no surprise in May 2012 when a majority of Netanyahu's own defense chiefs opposed an Israeli strike on the mullahs' nuclear facilities. That same month, the New York Times reported that Israel's former intelligence chief Meir Dagan "has said that a strike on Iran's nuclear installations would be 'a stupid idea,' adding that military action might not achieve all of its goals and could lead to a long war." Why?

"A strike could accelerate the procurement of the bomb," claimed Dagan, who spoke at a conference held at the National Security Studies Institute in Tel Aviv. "An attack isn't enough to stop the project."
Dagan posited that military action would align the Iranian population behind the regime, thus solving the country's political and financial problems. Moreover, he asserted that in the case of an Israeli strike, Iran could declare before the world that it was attacked even while adhering to agreements made with the International Atomic Energy Agency - by a country that reportedly possess "strategic capabilities."
"We would provide them with the legitimacy to achieve nuclear capabilities for military purposes," he said.

Short of a large-scale invasion and occupation of Iran by American forces, U.S. military action might still only delay the Iranian bomb Tehran would doubtless go into overdrive to produce. That's why former Bush Defense Secretary Bob Gates and CIA head Michael Hayden raised the alarms about the "disastrous" impact of supposedly surgical strikes against the Ayatollah's nuclear infrastructure. As the New York Times reported in March 2012:

A classified war simulation held this month to assess the repercussions of an Israeli attack on Iran forecasts that the strike would lead to a wider regional war, which could draw in the United States and leave hundreds of Americans dead, according to American officials.

And the costs in lives and treasure would be staggering. In November 2012, the Federation of American Scientists estimated that a U.S. campaign of air strikes would cost the global economy $700 billion; a full-scale invasion could have a total impact of $1.7 trillion. Two months earlier, a bipartisan report including signatories Brent Scowcroft, retired Admiral William Fallon, former Republican Senator and Pentagon chief Chuck Hagel, retired General Anthony Zinni and former Ambassador Thomas Pickering warned Americans about the cost of trying to eliminate the Iranian nuclear program once and for all:

A unilateral Israeli attack would set back the Iranian nuclear program by only 2 years and an American attack by 4 years. But if the objective is "ensuring that Iran never acquires a nuclear bomb," the U.S. "would need to conduct a significantly expanded air and sea war over a prolonged period of time, likely several years." In order to achieve regime change, the report says, "the occupation of Iran would require a commitment of resources and personnel greater than what the U.S. has expended over the past 10 years in the Iraq and Afghanistan wars combined."

The anticipated blowback?

Serious costs to U.S. interests would also be felt over the longer term, we believe, with problematic consequences for global and regional stability, including economic stability. A dynamic of escalation, action, and counteraction could produce serious unintended consequences that would significantly increase all of these costs and lead, potentially, to all-out regional war.

After reviewing the results of a 2004 war gaming exercise conducted by The Atlantic in conjunction with leading national security experts, James Fallows last month was moved to ask, "Would a U.S. Strike Against Iran Actually Work?"

Israel doesn't have the military capacity to "stop" Iran from getting a nuclear weapon, and neither does the United States, at least not in circumstances short of total war.

If this all sounds like the hypothetical scenarios of a bunch of doves in the Pentagon and the State Department, it is worth recalling the America reaction to the 1996 bombing of the Khobar Towers in Saudi Arabia which killed 19 U.S. servicemen and wounded hundreds of others. As former Clinton and Bush counter-terrorism chief Richard Clarke recounted in his book, Against All Enemies, President Clinton and the Joint Chiefs contemplated a massive U.S. invasion of Iran in response to the involvement of its agents:

In our meeting with the Pentagon in 1996, Shali was talking about al-out war. The military had a plan for almost any contingency. The plan on the shelf for war with Iran looked like it had been drawn up by Eisenhower. Several groups of Army and Marine divisions would sweep across the country over the course of several months.

Ultimately, President Clinton opted against the invasion of Iran, in part because of the difficulty in proving the U.S. intelligence case against Tehran to the international community. In the end, the U.S. launched a large-scale covert action campaign against Iranian intelligence assets worldwide. Apparently, the message was received with zero distortion; Iran has not targeted United States interests since.
But reducing to zero the risk of potential Iranian nuclear weapons is a challenge that differs in kind and degree from that President Clinton faced. Short of all-out war, only a diplomatic solution offers the chance to prevent Iran's actual deployment of atomic devices. Nevertheless, some Republicans and their allies in the conservative echo chamber are eager to call for that war today.
They just won't say what happens the day after.