By the blacklisting Tuesday, Dec. 11, of the Jabhat al-Nusra group fighting in Syrian rebel ranks as “a foreign terrorist organization” and affiliate of al Qaeda in Iraq, Washington faces four quandaries:

1. The 10,000 fighters of this al Qaeda affiliate are the best-trained and most professional component of the Syrian rebel front;.

2. Jabhat al-Nusra fields 3,000 fighters out of the mostly Free Syrian Army’s 14,000 rebels fighting in and around Aleppo. They also constitute the assault force’s spearhead.

3. The Islamists are at the sharp front edge of the rebel force battling for control of the Syrian army’s biggest chemical weapons store at Al Safira, near Aleppo. Thursday morning, Dec. 12, they were just a kilometer from the base’s northwestern perimeter fence and advancing fast. By week’s end, Jabhat al-Nusra jihadis may have smashed into the base and seized control of the chemical stocks and Scud D planes standing there armed with chemical warheads.

The imminence of this peril forced Bashar Assad’s hand into sending Scud jets against rebel-held areas in an effort to stop their advance on the base.

4.  This al Qaeda affiliate is also better armed and equipped than any other Syrian rebel force, thanks to the generous financial and logistical aid laid on by Persian Gulf sources, especially in Saudi Arabia, Qatar and Kuwait.

The difficulty here is that those three Gulf Arab states are also American allies in the war against Assad and the most important contributors to the US-sponsored Friends of Syria, a forum which met in Marrakesh Wednesday and formally recognized the umbrella Syrian opposition coalition of exiled groups as the legitimate government of Syria.

Reporters inside Syria reported that when the Jabhat al-Nusra fighters heard this news, they declared 700 of their number had died… laughing.

But as the vicious civil war of nearly two years and more than 40,000 dead approached another dangerous peak, no one was laughing in Damascus or Washington.

debkafile’s military sources point to the next crisis looming ahead: If Assad fails to stop the al Qaeda fighters from reaching Al-Safira and its poison gas stores - and an al Qaeda affiliate succeeds for the first time in arming itself with chemical weapons - the United States will have to mount an air assault – not on Assad’s army but on the Syrian rebel forces fighting him, because if they do manage to seize control of the base, rebel fighters may decide to send the chemicals-tipped missiles against Assad regime centers in Damascus.

The fall of al Safira would then transform the Syrian civil conflict into a chemical missile war.