Even as American and international negotiators were finalizing the interim agreement with Iran over its nuclear program, both houses of Congress were moving to tie President Obama's hands in the future. While a bipartisan bill mandating harsh new sanctions nears a veto-proof majority in the Senate, House Republicans announced they would take up the legislation championed by Senators Mark Kirk (R-IL) and Robert Menendez (D-NJ).
But the "Nuclear Weapon Free Iran Act" doesn't just risk fracturing the multinational coalition and scuttle its efforts to reach a final deal to control Tehran's nuclear program. It makes an American conflict with Iran much more likely. For starters, the text essentially commits the U.S. to come to Israel's defense even in a preventive war it chooses to initiate. South Carolina Senator Lindsey Graham (R-SC) among others has been threatening to bring the needed authorization for the use of military of force (AUMF) to the floor for months. All that's missing for hawks like Kirk warning of a repeat of Munich is the tax revenue to pay for the war they seem on a path to start.
If the United States learned anything from its preventive war in Iraq, it should have been that such misadventures are unpredictable, bloody and very, very costly. (Paul Wolfowitz's promises notwithstanding, the $1 trillion-plus price tag for the invasion and occupation was not paid for by "a country that could really finance its own reconstruction, and relatively soon.") In that regard, an American conflict with Iran would likely be little different.
Even if the Israelis alone launched a strike against Tehran's atomic sites, the ensuing Iranian retaliation against Israeli and American interests would almost certainly trigger the commitment of U.S. forces anyway. While Israel would face certain retaliation from Hezbollah rockets launched from Lebanon and Hamas missiles raining down from Gaza.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.

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.
All of which is why it's time for Republicans and Democrats alike so committed to stopping Iran's development of a nuclear weapons capability to put their money where their mouths are. Or more accurately, the taxpayers' money. If they are so serious about risking war with Iran, the very least they could do is ask the American people to pay for it.