Just what are we getting into in Syria?

It's hard to assess President Obama's decision to send arms to the Syrian rebels, because we still don't know what kinds of arms he's sending, how long he's willing to keep the stuff flowing or what kind of outcome he's seeking — both to the civil war in Syria and to the political balance in the region.

Still, a few things are clear about this new stage of U.S. military involvement.

First, this is not about "humanitarian intervention." A few news reports have attributed Obama's sudden shift on the issue to the recent ascension of Susan Rice as his national security adviser and Samantha Power as his U.N. ambassador. But no pair of advisers can make such a dramatic impact on policy so swiftly — especially in this White House, where the president sets the tone on foreign policy and national security.

Nor is it about the Syrian army's use of chemical weapons, although Obama's oft-repeated statements that the use of chemical weapons would cross a "red line" have put him in a situation where he had to do something, lest he lose credibility on other pledges and threats. True, U.S. intelligence agencies have firmed up their conclusion that the traces of sarin gas can be traced to Bashar Assad's regime — but their verdict was pretty firm several weeks ago.

Fundamentally, Obama's shift is about balance-of-power politics. His deputy national security adviser, Ben Rhodes, said as much at the June 14 White House news conference where he announced the new policy. The decision to provide "dramatically increased assistance" to the armed rebels took hold, he said, "as we saw a deteriorating situation in general, with outside actors like Iran and Hezbollah getting involved."

Rhodes did not specify what kinds of weapons Obama will provide; Obama himself may not yet know. But it is clear that, whatever gets shipped, weapons are only part — and perhaps not the most important part — of the package. Speaking of the rebel forces, Rhodes said it was important to "strengthen their cohesion," to turn these "disparate groups of opposition fighters in different parts of the country" into an "organized opposition."

In other words, he's talking about command and control, communications, intelligence, logistics — the connective tissues of warfare, which only an outside professional military power can provide.

This tissue is political as well as military. As Rhodes put it, "We want to connect [the rebels] to us, but also to our other partners who are providing assistance," including Jordan, Saudi Arabia, the United Arab Emirates, Qatar and Turkey. All those countries want to help the rebels — if just to stave off the expansionist ambitions of Iran — but they have shown little knack for working together on such matters. The United States can coordinate. Some of Obama's critics ridicule this as "leading from behind," but sometimes (for example, in Libya) it can work.

What is Obama's endgame in this? That's less clear, or rather it's not clear whether the endgame is feasible. At his news conference, Rhodes put it this way: "We still continue to discuss with the Russians whether there is a way to bring together elements of the [Assad] regime and the opposition to achieve a political settlement."

There is no notion here of a rebel victory; nor is Obama doing anything to suggest that this is his goal. A successful outcome, Rhodes said, would be a "political settlement" — preferably forged and imposed by the United States and Russia together — that pushes Assad out of power but "preserves some elements of the regime" while also bringing in "the opposition, who we believe speaks for the majority of the country."

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This is, to say the least, far-fetched. Russia regards Assad as an ally, his regime as a bulwark of Russian geostrategic interests and any opening to the opposition as a source of dangerous instability. Rhodes acknowledges the difficulty, but notes that what the Russians want least of all is "a downward spiral" in which the region grows more "chaotic" with "extremist elements gaining a foothold in Syria."

Again, the chances seem dim. The scenario assumes that, faced with a more cohesive, American-assisted rebel army, the Syrian army will come under crippling attacks and that, as a result, the Syrian government will be forced to the negotiating table. It is equally or more likely, of course, that the Syrians will respond by stepping up the destruction and that the Russians will accelerate the delivery of their arms.

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Which leads back to the original question: Just how much is Obama willing to put into this battle, and for how long? At this point, the answer seems to be: not much. "The one option that we basically have taken off the table," Rhodes said, "is boots on the ground" — and a good thing, too. There is some talk of imposing a no-fly zone on the Syrian air force, but the Joint Chiefs are leery and Obama has not approved such an option. If he does, Rhodes assured the reporters, he would discuss it publicly "in some detail."

I am not so worried, as some liberal (or anti-interventionist) critics are, that Obama's decision to arm the rebels may be the first step on a "slippery slope." Whatever else one might say about Obama, he seems immune to slippery slopes. In Libya, he did what he said he would do (which amounted to quite a lot of firepower), and no more. In Afghanistan, he acceded to the Joint Chiefs' request for 33,000 more troops — but then gave them no more, and began to withdraw the whole lot, when they failed to meet the goals that his generals said they'd meet within 18 months. He is extremely alert to the dangers of uncontrolled escalation.

And yet it's unclear what he realistically hopes to accomplish with this step and what further steps he might take if it doesn't do the job. It's also unclear how broadly he views this conflict and our role in it. Is the goal simply to stabilize Syria? Or does he also view the civil war as one piece of a regionwide Sunni-Shia conflict? (Clearly, the other interested outside powers do.) And in what way does he think his policies might exacerbate — or mitigate, reroute or tone down — this larger, conflict? Or is he stepping into this deep muddy only to keep the Shia side, chiefly Iran and Hezbollah, from gaining too much strength? In which case, won't this just ratchet up the violence and swell the death toll?