“The Syrian regime’s policy of maintaining power by terrorizing its people only indicates its inherent weakness and inevitable collapse,” said a statement issued by Obama last Saturday. “Assad’s fall is inevitable.  It’s clear his regime is no longer in full control of the country and only continues to take Syria toward adangerous end,” National Security Council spokesman Tommy Vietor told my colleague David Ignatius ten days ago.

But what if Assad’s defenses — including the tanks and artillery of his Republican Guard and elite Fourth Armored division — are made of brick? That’s what it’s beginning to look like this week as the regime pounds rebel-held neighborhoods in the city of Homs, killing hundreds a day. The rebel Free Syrian Army — a hodgepodge of neighborhood militias and defected soldiers armed with light weapons — seems to lack the capacity to stand up to such an assault, much less defeat it.

The onslaught in Homs, along with the veto by Russia and China of a United Nations Security Council resolution last weekend, have prompted Sens. John McCain (R-Ariz.), Lindsey Graham (R-S.C.) and Joseph Lieberman (I-Conn.) to propose that the United States and its allies begin actively aiding the Syrian opposition, including with weapons. The White House and State Department demur: “We don’t think more arms into Syria is the answer,” said State.

To which McCain tweeted Thursday: “Tell that to the Iranians and Russians.” Both have provided materiel aid to Assad’s forces.

The administration’s theory seems to be that Assad’s army will soon be exhausted by defections and the impossibility of suppressing opposition across the country. Its generals — maybe after listening to Washington’s predictions? — will turn on Assad, depose him, and then accept the Arab League’s plan for a democratic transition.

Yet Assad’s top generals, like him, are members of the minority Alawite clan; the commander of the Fourth Division is his brother, Maher. These men may feel they have nowhere to go in a country and a region where Sunni Islamists are in the ascendancy, and no choice but to fight to the bitter end. Not possible? Ask their enemies in Lebanon, the Maronite Christians, who played out a losing hand for 14 years of civil war in the 1970s and 80s.

Either an Assad victory or a long war would be a disaster for the United States and its allies; a speedy collapse of the regime would be a devastating blow to Iran, for which Syria is a crucial ally. It follows that the best U.S. policy — in what is, at best, a bad and risky situation — is to follow McCain’s advice. This could be easily done through proxies: Persian Gulf states, and possibly Turkey, are already providing aid and probably arms to the Free Syrian Army.

A senior European diplomat I spoke with today shuddered at this prospect: The EU, like the State Department, favors forming a “Friends of Syria” group with the Arab League that would do...well, it’s not yet clear. But the diplomat said an arm-the-opposition policy would trigger unforseeable blowback — another Afghanistan.

That’s a misreading of history. In fact, arming the Afghan opposition in the 1980s succeeded in its aim of driving out the Soviet Union. U.S. responsibility for the subsequent chaos lay in its abandonment of the country after 1989, not the arms it gave the mujahadeen.

In this case, the United States has reason to provide material support for the Syrian opposition precisely so it can be a player in Syria if and when Assad does fall. Western influence could be vital in shaping the post-Assad regime. Or would it be better to stand back while Saudi and Qatari fundamentalists ship weapons to their counterparts in Syria — and call the political shots afterward?