For every action, there is an equal, and opposite reaction. This is true in physics as well as foreign policy.

When it became clear that President Obama would increase our assistance to the Syrian rebels, the terrorist group Hezb'allah pre-empted the president and sent thousands of fighters to Syria. They promptly helped the Syrian army score a huge victory by capturing a strategic city Qusair, and now their leader, Hassan Nasrallah, has vowed to continue the battle now that America will be arming the rebels:

Sheikh Hassan Nasrallah, chief of the Shiite Hezbollah group in Lebanon, appeared unwavering in his support for the regime of Syrian President Bashar Assad.

He signaled for the first time the Iranian-backed militant group will stay involved in the civil war after helping Assad's army recapture the key town of Qusair in central Homs province from rebels.

"We will be where we should be. We will continue to bear the responsibility we took upon ourselves," Nasrallah said in a speech via satellite to supporters in south Beirut. "There is no need to elaborate. ... We leave the details to the requirements of the battlefield."

Nasrallah appeared angry and defiant, saying the group has made a "calculated" decision to defend the Assad regime.

And now, the other shoe has dropped. In the wake of President Obama's decision to arm the rebels, Iran will send 4,000 troops to Syria to bolster the Assad regime:

Washington's decision to arm Syria's Sunni Muslim rebels has plunged America into the great Sunni-Shia conflict of the Islamic Middle East, entering a struggle that now dwarfs the Arab revolutions which overthrew dictatorships across the region.

The Independent on Sunday has learned that a military decision has been taken in Iran - even before last week's presidential election - to send a first contingent of 4,000 Iranian Revolutionary Guards to Syria to support President Bashar al-Assad's forces against the largely Sunni rebellion that has cost almost 100,000 lives in just over two years.  Iran is now fully committed to preserving Assad's regime, according to pro-Iranian sources which have been deeply involved in the Islamic Republic's security, even to the extent of proposing to open up a new 'Syrian' front on the Golan Heights against Israel.

For the first time, all of America's 'friends' in the region are Sunni Muslims and all of its enemies are Shiites. Breaking all President Barack Obama's rules of disengagement, the US is now fully engaged on the side of armed groups which include the most extreme Sunni Islamist movements in the Middle East.

Consider: the only reasons for American intervention in Syria are to shorten the war and contain the conflict so that it doesn't become a region-wide conflagration. Instead, our arming the Syrian rebels will not prove decisive in any way, potentially prolonging the conflict by marginally improving rebel forces, and the reaction to our intervention may set off a wider war that may engulf the entire Middle East.

Congress has a right and a duty to put its foot down to stop this ill-advised intervention.