As 2013 draws to close, the negotiations over the Iranian nuclear program have entered a delicate stage. But in 2014, the tensions will escalate dramatically as a bipartisan group of Senators brings a new Iran sanctions bill to the floor for a vote. As many others have warned, that promise of new measures against Tehran will almost certainly blow up the interim deal reached by the Obama administration and its UN/EU partners in Geneva. But Congress' highly unusual intervention into the President's domain of foreign policy doesn't just make the prospect of an American conflict with Iran more likely. As it turns out, the Nuclear Weapon Free Iran Act essentially empowers Israel to decide whether the United States will go to war against Tehran.
On their own, the tough new sanctions imposed automatically if a final deal isn't completed in six months pose a daunting enough challenge for President Obama and Secretary of State Kerry. But it is the legislation's commitment to support an Israeli preventive strike against Iranian nuclear facilities that almost ensures the U.S. and Iran will come to blows. As Section 2b, part 5 of the draft mandates:

If the Government of Israel is compelled to take military action in legitimate self-defense against Iran's nuclear weapon program, the United States Government should stand with Israel and provide, in accordance with the law of the United States and the constitutional responsibility of Congress to authorize the use of military force, diplomatic, military, and economic support to the Government of Israel in its defense of its territory, people, and existence.

Now, the legislation being pushed by Senators Mark Kirk (R-IL), Chuck Schumer (D-NY) and Robert Menendez (D-NJ) does not automatically give the President an authorization to use force should Israel attack the Iranians. (The draft language above explicitly states that the U.S. government must act "in accordance with the law of the United States and the constitutional responsibility of Congress to authorize the use of military force.") But there should be little doubt that an AUMF would be forthcoming from Congressmen on both sides of the aisle. As Lindsey Graham, who with Menendez co-sponsored a similar, non-binding "stand with Israel" resolution in March told a Christians United for Israel (CUFI) conference in July:

"If nothing changes in Iran, come September, October, I will present a resolution that will authorize the use of military force to prevent Iran from developing a nuclear bomb."

Graham would have plenty of company from the hardest of hard liners in his party. In August 2012, Romney national security adviser and pardoned Iran-Contra architect Elliott Abrams called for a war authorization in the pages of the Weekly Standard. And just two weeks ago, Norman Podhoretz used his Wall Street Journal op-ed to urge the Obama administration to "strike Iran now" to avoid "the nuclear war sure to come."
But at the end of the day, the lack of an explicit AUMF in the Nuclear Weapon Free Iran Act doesn't mean its supporters aren't giving Prime Minister Benjamin Netanyahu de facto carte blanche to hit Iranian nuclear facilities. The ensuing Iranian retaliation against to Israeli and American interests would almost certainly trigger the commitment of U.S. forces anyway.
Even if the Israelis alone launched a strike against Iran's atomic 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. Israel would face certain retaliation from Hezbollah rockets launched from Lebanon and Hamas missiles raining down from Gaza.
That's why former Bush Defense Secretary Bob Gates and CIA head Michael Hayden raising the alarms about the "disastrous" impact of the 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 that September, a bipartisan group of U.S. foreign policy leaders including Brent Scowcroft, retired Admiral William Fallon, former Republican Senator (now Obama Pentagon chief) Chuck Hagel, retired General Anthony Zinni and former Ambassador Thomas Pickering concluded that American attacks with the objective of "ensuring that Iran never acquires a nuclear bomb" would "need to conduct a significantly expanded air and sea war over a prolonged period of time, likely several years." (Accomplishing regime change, the authors noted, would mean an occupation of Iran requiring 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.

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.)
The Pentagon's 2012 war-gaming in a simulation called "Internal Look" served to reinforce for U.S. military officials "the unpredictable and uncontrollable nature of a strike by Israel, and a counterstrike by Iran." As for the impact on the global economy, in November, the Federation of American Scientists estimated that a U.S. campaign of air strikes would cost $700 billion; a full-scale invasion could have a total impact of $1.7 trillion.
At the heart of the clash between Congressional hawks and President Obama is a disagreement over the so-called "red line" for Tehran. In the United States and in Israel alike, Obama has said the United States will not allow Iran to obtain an actual nuclear weapon. But most of his Republican foes and some of his Democratic allies have sided with Bibi Netanyahu in demanding Iran never possess a "nuclear weapons capability." That bottom line on Iranian nuclear know-how wouldn't just scuttle the interim deal and ongoing negotiations with Tehran, as the Obama administration and 10 Democratic Senate committee chairmen have warned. By the standard, an American war with Iran would be almost a foregone conclusion. And if Chuck Schumer, Bob Menendez, John McCain, Lindsey Graham and over 30 other Senators get their way, Israel may well have a green light to start it.