Is Hamas responsible for Gaza rocket fire? Not exactly.

And there could well be more of it without them.

Israel's air offensive on the Gaza Strip today is a response to rocket fire from the coastal Palestinian enclave. Hamas, which governs the strip, has borne the brunt of the assault. The action began with a missile that targeted Hamas military leader Ahmed Jabari as he drove through Gaza City today (the IDF quickly shared a video of that attack) and was followed by dozens more. 

Here's how Israeli Ambassador to the US Michael Oren explained the Gaza strikes this afternoon: "The scope of the IDF's defensive operation depends on Hamas and whether it takes the decision to cease firing missiles on our homes."

But Hamas has not been the principal one firing the rockets at Israel, at least not lately. Other, smaller militant groups in Gaza like Islamic Jihad and the popular resistance committees in the strip do much of the shooting, though the Al Qassam Brigade that Mr. Jabari headed until his death has taken credit for some attacks in recent weeks.

This may be a distinction without a difference to Israeli officials. They frequently argue that Hamas is the governing authority in Gaza, and therefore is de facto responsible for all rocket fire.

But Hamas has in fact been trying to keep rocket fire under control in the years since Israel's Operation Cast Lead in the territory in late 2008/early 2009. One of their most important men in keeping militancy under wraps? Mr. Jabari, who was powerful enough and respected enough to prevent a major outbreak of violence from Gaza that could have invited powerful reprisals.

Here's how veteran Israeli columnist Aluf Benn put it today:

Ahmed Jabari was a subcontractor, in charge of maintaining Israel's security in Gaza. This title will no doubt sound absurd to anyone who in the past several hours has heard Jabari described as "an arch-terrorist," "the terror chief of staff" or "our Bin Laden." But that was the reality for the past five and a half years. Israel demanded of Hamas that it observe the truce in the south and enforce it on the multiplicity of armed organizations in the Gaza Strip. The man responsible for carrying out this policy was Ahmed Jabari.

Now Israel is saying that its subcontractor did not do his part and did not maintain the promised quiet on the southern border. The repeated complaint against him was that Hamas did not succeed in controlling the other organizations, even though it is not interested in escalation. After Jabari was warned openly (Amos Harel and Avi Issacharoff reported here at the beginning of this week that the assassination of top Hamas people would be renewed), he was executed on Wednesday in a public assassination action, for which Israel hastened to take responsibility. The message was simple and clear: You failed - you're dead.

Hamas control of the strip was never ironclad, and it could well get worse from here on out. Under the best of conditions, Hamas has had a politically understandable reluctance to target Palestinian militants who seek to strike out at Israel. A majority of the strip's population are descendants of refugees who were forced out of their homes in 1948, and the rocket-fire now falls in the areas where their ancestors formerly lived.

Hamas's rise to power there was thanks in equal measure to the widespread corruption of Fatah and to Hamas's image as a more serious and committed resister of Israel than its secular rival. So there are political costs to shutting down the militant groups that fire rockets at Israel, not to mention that such efforts could escalate into a civil war. Though Israel publicly seems to assert that Hamas can simply turn of the rocket attacks if it chooses too, the reality in Gaza is a bit more complex.

Now, Hamas will be mulling whether it should retaliate with some of the longer-range rockets from their arsenal. The argument against that would be Israel's overwhelming military advantage, which would be brought down hard on Hamas leaders, the rank and file, and average Gaza residents alike. The Hamas deal with Israel in recent years – restraining rocket attacks – has been to its own advantage. While taking a tough stance against Israel is generally popular, provoking the powerful neighbor with tactically useless rocket-fire, is not, particularly since Israel's response cause so much misery among Gaza's population.

That logic still holds, as furious as the group must be about the attacks today. So far, the message from Hamas has been fairly restrained.

Spokesman Sami Abu Zuhri said in a statement: "I warn those who violate all laws and accords of grave consequences if they persist in this unprovoked aggression. The resistance has the full right to respond, to provide security and protection for the Palestinian people in the face of these repeated murderous raids." Declaring a right to respond is something different than promising a response.