As the Obama administration debates belatedly arming the Syrian opposition, military analysts are arriving at an uncomfortable conclusion: the U.S. can't hand the rebels guns or rockets and expect them to topple dictator Bashar Assad. In fact, it may never happen.

Yes, the U.S. can provide lots of hardware, from shoulder-fired anti-aircraft missiles to communications systems to armored vehicles. That military gear can prolong the conflict, preventing dictator Bashar Assad from crushing the rebels. It is unlikely to tip the balance of the war toward the rebels so they can decisively overthrow Assad.

Obama is considering a range of weaponry to the rebels, as described in the Washington Post, including surface-to-air missiles. The idea would be to ship them the weapons, bolster their war effort, and watch them topple the blood-soaked dictator – without a deeper U.S. military commitment.

Except that few strategists consider that realistic. Assad has a variety of advantages – an adaptive military estimated at over 50,000; complete air superiority; chemical weapons – that he will retain even if Obama opens a new arms pipeline. Overcoming those advantages means getting, at the least, U.S. and allied airpower involved – a step the Obama administration, and especially the military, want to avoid. Especially since it might involve shooting down Iranian planes, a fateful step.

"The Syrian regime is not collapsing, nor is it on the verge of collapse," says Christopher Harmer, a former U.S. Navy officer and analyst with the Institute for the Study of War. "Everyone has been saying that for about 18 months. It has contracted, and may be forced to contract further; as long as they have control of their chemical weapons, I don’t think there is a collapse scenario."

In Harmer's tally, there are a number of weapons systems the U.S. can provide the rebels, in great volume and low cost. The U.S. Single Channel Ground and Airborne Radio System, a combat net radio that U.S. and allied troops use for transmitting voice and data, would enhance rebel communications and control over their makeshift soldiers. Humvees and five-ton M939 trucks can help mitigate the rebels' transportation problems without being so large and ponderous that they're easy targets for Assad's air power. Anti-armor weapons like the AT-4 or the FGM-148 Javelin can assault his armored vehicles, and the iconic Stinger shoulder-mounted missile will make Assad's planes and helicopters think twice about flying over rebel-held territory. Together, that weaponry would pressure Assad significantly.

But the most all those weapons could accomplish would be to force Assad "to cut out Aleppo," Harmer concedes. His forces would retrench to the Mediterranean coastal areas and down southward to Damascus, remaining in power. The stalemate would continue – along with pressure for the U.S. to dig deeper into the conflict.

"There's frustration in Washington about being pushed from behind," says Aram Nerguizian, who analyzes the Syria conflict for the Center for Strategic and International Studies. "You've got an [administration] effort to try and appear to do more, but beyond that there's a real fear – there's no reason, as far as the U.S. is concerned, to inherit yet another civil conflict in the Mideast."

There's another option, one several senators have called for: using American and allied air power to take away Assad's control of the skies. However you construct a no-fly zone – launch Tomahawk missiles from submarines in the Med against Syria's recently upgraded air defenses; use the U.S.Patriot missile battery in Turkey as the basis for an anti-aircraft effort; scramble F-15s, F-16 or F-22s; whatever – it takes away "an indespensible element of Assad-regime survival," Harmer argues. The important thing is to stop the Iranian planes filled with weapons and stop the Beechcraft-sized Syrian planes from conducting aerial intra-theater resupply of Syrian Army forces.

Harmer contends that a no-fly zone wouldn't have to become a foreign-provided Free Syrian Air Force: U.S. pilots won't have to provide close-air support for rebel forces or bomb ground targets. But from Harmer's perspective, once Assad's air power is blunted, "the only solution left is a negotiated conclusion, or, more likely, a fallback to the Alawite coastal areas." In other words, the Assad regime as we know it is over.

It's an optimistic assessment: many, many analysts have considered airpower the key to breaking an enemy's will, and many analysts have been refuted. It's possible – but it depends on Assad suing for peace, not a suddenly invincible Syrian rebel force on the ground. And its risks are substantial: not least of which, it would mean American pilots shooting down Iranian resupply planes, an act of war. "I don't envy President Obama's decision," Harmer says.

The open secret in Washington is that Syria is a war the U.S. military does not want to fight. (Even if other government agencies are active in the conflict.) Yesterday, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, said that Syria's air defenses could be overcome for a no-fly campaign, but not without endangering U.S. pilots and at greater campaign length than the 2011 Libya no-fly zone. Last month, his boss, Defense Secretary Chuck Hagel, warned Congress about getting bogged down in Syria.

"We've been sucked into this open-ended arrangement before, and we're not going there again," an anonymous senior U.S. officer told the New York Times last year. The Air Force chief of staff, Gen. Mark Welsh, recently warned that that while he'd use the unproven F-22 in Syria, his Air Force is spread thin: "there aren't many airplanes. In this business, quantity does have a quality all its own." The military estimated needing 70,000 troops on the ground to secure Syrian chemical weapons alone, a force larger than the one in Afghanistan, and the Pentagon's preference is to only go after those weapons at the behest of a post-Assad government. Lurking in the background: should Obama Americanize the war in the air, and it fails to topple Assad, how will he avoid pressure to use ground troops?

All of this ignores fundamental issues like who governs a post-Assad Syria or how to keep U.S. military aid for the Syrian rebels out of the hands of the faction of fighters aligned with al-Qaida. But it illustrates two things. First, there isn't a magic menu of weapons Obama can give that will lead to a rebel victory; missiles, radios and trucks can draw the conflict out longer but not end it on favorable terms. Second, even a move as seemingly low-cost as arming the rebels risks escalating into a commitment the U.S. can find it hard to end. Obama should have thought about that before he started talking about red lines.