With Syrian rebel forces gaining in strength, elite units loyal to Bashar Assad received a frightening order a few weeks ago: begin preparations that could lead to the use of chemical weapons.

There was evidently no order to actually execute a chemical attack, which would be the first deadly gassing in the Mideast in almost 25 years. Nor is it clear who gave the order to prep the chemical stocks. But new information is emerging about why the U.S. government recently warned Assad against using his unconventional arsenal.

Danger Room first reported last week that U.S. officials recently saw indications that at least some Syrian military forces mixed precursor chemicals for sarin gas, which got the weaponized stocks to the point where they could be loaded onto planes and dropped. The Washington Post's Joby Warrick adds detail to that account. Some elite troops received "specific orders" to prep the weapons. At least one Syrian army unit was caught on surveillance photos loading "special military vehicles" that could be used to transport the weapons.

Those preparations came to a halt last week: There is apparently no evidence that "activated chemical weapons" were loaded onto military planes or sent near rebel positions. Syria has apparently begun firing ballistic Scud missiles at rebel-held areas, but while the Scuds are capable of carrying a chemical payload, they've not done so yet. Defense Secretary Leon Panetta told reporters this week that the U.S. hasn't seen new indications of a potential chemical attack. (Which may be a statement about the status of U.S. surveillance efforts, not Assad's unconventional weapons stocks.) But Warrick writes that there were fears throughout the U.S. intelligence community that "a single commander could unleash the deadly poisons without orders from higher up the chain of command." The chairman of the House intelligence committee, Rep. Mike Rogers (R-Mich.), told Reuters the chemical weapons "could be used at a moment's notice, which is very different from before."

That fear heightens with concerns that the Assad regime is living on borrowed time. Once combined, Assad's sarin stocks are good for perhaps as long as a year, so those commanders don't have to fear that they've got to use the chemical weapons or lose them. "If the situation becomes more desperate," an anonymous Western diplomat tells Warrick, "there's no predicting what will happen."

But the end of the Assad regime may not be nigh after 20 months of fighting. An analyst at the well-connected Eurasia Group, Ayham Kamel, assesses that the loyalist forces are prepping a "new strategy" of consolidating strength around urban areas under their control. They still have the advantage of air power, even with the rebels' air-defense weaponry and a big artillery advantage against the rebels' DIY rockets. Still, even with those advantages, Kamel assesses Assad will only last until mid-2013: one of its major allies, Russia, now has an ambiguous stance on its faith in Assad's ability to withstand the insurgency.

Meanwhile, the U.S. is putting skin into the game. Not only will it bring Patriot missile batteries to southeastern Turkey, under NATO auspices, but it's deploying 400 U.S. troops to help operate them. That's hardly an invading force. But it's functionally a tripwire: should Assad fire Scuds into Turkey, he'd risk killing or injuring Americans, which would surely prompt calls for retaliation. Diplomatically, President Obama announced he'd recognize a new rebel coalition as the legitimate government of Syria – one that excludes the Jabhat al-Nusra, which the U.S. considers an al-Qaida-linked terrorist group – and the U.S. Agency for International Development is contracting out for a "transition" officer based in Turkey who can help guide the coalition into something capable of governing.

Still, the Syrian opposition remains a fractious one. Some rebels are dissatisfied at the U.S. listing the Jabhat al-Nusra as a terrorist group, since it's apparently an effective fighting force. (It also takes rhetorical shots at WordPress, the company that makes its website's content management system, for suspending its account over a terms-of-service violation.) Lack of rebel cohesion is a major reason why the Eurasia Group's Kamel thinks Assad holds a stronger hand than typically believed: it's "prevented the opposition from consolidating on military successes, which have then often proved transient."

There hasn't been a chemical attack in the Middle East since Saddam Hussein gassed Iraqi Kurds at Halabja in 1988. Assad's motivations remain unclear to U.S. officials, but according to Warrick, someone in the Syrian chain of command provided instructions to prep sarin for potential battlefield use about two weeks ago. Assad's intentions are unknowable, but using sarin will most foreclose on the life-saving option of finding a foreign country willing to accept Assad for exile. Then again, an anonymous Mideastern intelligence official told Warrick, "If you're a general and you think you’re not going to survive this, you might not care."