I think we could get away with just arms supplies to rebels and humanitarian aid to civilians in areas outside of Assad's control.
I assume we'd help with air defense for Turkey and Jordan with both fighter aircraft and anti-aircraft missiles.
I also assume that Syria will be the new home of the "special forces Olympics" where special forces from us and many of our allies operate to support rebels.
The question is whether we jump in with a no-fly zone or air strikes over Syria.
I assume large numbers of ground forces won't be sent since both Jordan and Turkey have armed forces well capable of taking on Assad's rebellion-weakened army. We would support both with air power, I assume, if needed.
But the question of what ground forces we might send to deal with chemical weapons is up in the air. I've recently read that air attacks could destroy chemical depots--contrary to what I'd read in the recent past--so maybe we wouldn't need much in the way of ground forces. Just sufficient forces in Jordan to protect air bases and headquarters and logistics elements, and provide a rapid reaction force to help special forces if they get in trouble inside Syria.
A reinforced Marine brigade might be the ticket. And maybe a paratrooper brigade and some Rangers flown in as the operation gets under way, plus an Army infantry brigade flown in if we move afloat prepositioned equipment for that brigade to Aqaba.
And President Obama has the justification he's long said he needs:
The United States and its allies have concluded that the government of Bashar al-Assad has used chemical weapons in Syria's protracted civil war, leading President Barack Obama to broaden aid — including military support — to opposition groups.
The intelligence community concluded with "high confidence" that the Assad regime had used chemical weapons — including the nerve agent sarin — "on a small scale against the opposition multiple times in the last year."
I suspect we downplayed the use to buy time to get ready to intervene.
UPDATE: I wrote this last night. This morning, the news is we will send arms to the rebels and are thinking about a limited no-fly zone in the south, based in Jordan:
The United States is considering imposing a no-fly zone in Syria, its first direct military intervention of the two-year-old civil war, Western diplomats said on Friday, after the White House said Syria had crossed a "red line" by using nerve gas.
After months of equivocating, President Barack Obama's administration said on Thursday it would now arm rebels, having obtained proof the Syrian government used chemical weapons against fighters trying to overthrow President Bashar al-Assad.
This news alone will boost the morale of the rebels.
To bypass the UN where Russia would veto a no-fly zone resolution (they won't make the mistake of Libya again), we may create a safe zone within Jordan so we could defend Jordanian air space to protect rebels training and arming inside Jordan before going north:
Citing unnamed U.S. military officials, the Wall Street Journal has reported that the Pentagon has developed a plan to bring the Syrian rebels across the border into Jordan, and then keep the Syrian air assets at bay with a limited no-fly zone.
Strategypage says it will be a bloody summer:
Western governments see increasing aid to the rebels as the least bad choice. The rebels still contain a lot of Islamic terrorist groups, and these outfits make no secret of their desire to continue the fight against Israel and the West in general. Dealing with these terror groups during the fight against the Assads, and after the Assads are defeated, is just a given. Deal with it as you go along and get rid of the Assads first, who are now considered the unequivocal greater evil. In any event the Islamic terror groups are doing what they usually do and making themselves unpopular among the civilians they are allegedly fighting to liberate. The terrorists attempt to impose strict lifestyles and are quick to execute suspected blasphemers or “spies”.
Assad seems to be looking north to Aleppo. If our aid is going to the rebels in the south, what will the northern rebels get? Will Turkey help up there?
While Hezbollah is heading north, too, there just aren't that many and they've already taken some heavy losses at Qusayr. I wonder how many battles they have in them.
And we'll see how those new pro-Assad militias hold up under heavier combat with rebels who will be better armed--and may have other help.