As Congress debates authorizing U.S. military strikes against Syria, it's worth remembering that President Obama has painted himself into a box with not one, but two red lines. After all, Obama didn't just casually announce that "a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized" by the Assad regime in Damascus The President also repeatedly promised Americans and Israelis that "America will do what we must to prevent a nuclear-armed Iran."
But while it is far from certain that a Congress badly fractured across party lines will approve Obama's proposal to punish Damascus for the red line Syria has already crossed, there's little doubt that the President would get the green light for a preventive war against Tehran and its nuclear program.
It should come as no surprise that President Obama would have no problem bringing along the hard liners of the Republican Party's neoconservative camp should he ask Congress to bless strikes against Iran. Even as the election of Hassan Rouhani renewed hopes for a peaceful resolution of the standoff over Tehran's nuclear ambitions, South Carolina Senator Lindsey Graham told a cheering audience at a recent Christians United for Israel conference:

"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."

Last year, the Romney-Ryan campaign was demanding the same thing. On Monday, Elliot Abrams, the same Iran-Contra architect who also helped birth the George W. Bush's invasion of Iraq, called on Congress to give President Obama the authority to launch attacks against Assad. But one year ago, the adviser to the 2012 GOP ticket wrote in the Weekly Standard that it was "time to authorize use of force against Iran."
Mercifully, Abrams' plea largely fell on deaf ears. But many of those in Congress who are balking at hitting Assad over his use of chemical weapons to massacre Syrian civilians have no qualms when it comes to a major confrontation with Iran. Representatives Michele Bachmann (R-MN) and Louie Gohmert (R-TX) were among the 100 Congressmen of both parties who recently signed a letter to President Obama asking him to see House and Senate blessing for his proposed retaliation against the Syrian dictator. But while Bachmann and Gohmert have made it clear they will oppose the use of force against Damascus now, they had no issue with saber-rattling towards Tehran in 2010. Along with the other 42 member of the House Tea Party caucus, they proposed a resolution which "supports using all means of persuading the Government of Iran to stop building and acquiring nuclear weapons" and declared:

[S]upport for Israel's right to use all means necessary to confront and eliminate nuclear threats posed by Iran, defend Israeli sovereignty, and protect the lives and safety of the Israeli people, including the use of military force if no other peaceful solution can be found within a reasonable time.

Aside from Rand Paul (who praised Bashar al-Assad's protection of Christians), the likely entrants in the 2016 GOP presidential race have largely been silent on President Obama's proposed authorization for the use of force (AUMF) against Syria. But when it comes to Iran, Marco Rubio and Ted Cruz have taken the same hard line. As the American Conservative posited, "it seems likely that they would oppose military strikes on Iran only if they were launched without consulting Congress."
But it's not just Republicans seemingly eager for confrontation with Iran. Just days after President Rouhani's inauguration in Tehran boosted hopes for a compromise with the U.S., the House by a 400 to 20 vote rebuffed the White House in passing a resolution calling for even harsher sanctions on Iranian oil exports. In September 2012, the Senate voted 90 to 1 for a nonbinding resolution rejecting containment as U.S. policy and accepting Prime Minister Benjamin Netanyahu's much lower "capability" threshold for military action. But not content to rule out "any United States policy that would rely on efforts to contain a nuclear weapons-capable Iran," a coalition of Senators led by Lindsey Graham (R-SC) and Robert Menendez (D-NJ) has also proposed a new resolution essentially green-lighting an Israeli assault on Iran and guaranteeing U.S. intervention. That resolution:

Urges that if Israel is compelled to take military action in self-defense, the United States will stand with Israel and provide diplomatic, military, and economic support in its defense of its territory, people, and existence.

Last year, former Defense Secretary Robert Gates had this to say about the prospect of a U.S. blank check for unilateral Israel action:

"That would be worse than us doing it. Because I think that then has lots of regional complications that may end up in a much larger Middle East conflict. So I think that would be worse."

Either way, the aftermath of strikes against Iran could be staggering. 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.) Last November, 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 (now 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."

To be sure, even limited American strikes on Syria could produce blowback, either from the Assad regime or its Hezbollah allies. Whether that comes to pass may now largely depend on which Republican urge--to lash out against President Assad or to humiliate President Obama--proves more powerful. Regardless, war with Iran over nuclear weapons it has neither used nor yet developed would be orders of magnitude worse. Nevertheless, should negotiations with Tehran falter, that is a course most in Congress seem ready to endorse if and when the time comes.