The primary targets of Israel's attack on Iran do not seem to be nuclear research and production facilities. People in the top positions of Iran's military forces, top scientists of Iran's nuclear program and political leaders seem to have been the primary aim.
Two dozen high ranking officers, including the chief of the General Staff of the Iranian Armed Forces, General Mohammad Bagheri, and the commander of the IRGC’s Aerospace Force, Amir-Ali Hajizadeh, were killed in targeted attacks. Several leading scientist were killed over night when Israel bombed the civilian buildings they were living in.
Iran's main nuclear enrichment facilities are buried underground near Natanz and Fordow. Satellite images show only light damage on above ground facilities in Natanz. Fordow seems to have not been attacked at all. There were attacks on some of Iran's ballistic missile facilities. There are no reports yet of the level of damage they received.
Curiously there were no signs of any active air defenses. Israel seems to have disabled them by other means than open warfare.
Israeli sources claimed that Iran had retaliated by launching a hundred drones against Israel. There were however no observations of any drone. Iranian sources say that none had been launched (yet).
The attacks so far seem to be aimed more at regime change than on nuclear facilities. The few strikes on nuclear infrastructure are just enough for Israel to claim this as an act of preemptive self-defense.
A preemptive self defense is legal under international law. But it requires that the threat is "instant", "overwhelming" and "imminent" leaving "no time for deliberation". None of these conditions existed when Israel launched its attack. The war it launched is thus an act of aggression and illegal under international law.
Israel has planned for the campaign to continued for at least two weeks:
Israel's operation against Iran's nuclear program, military leadership and arsenal of missiles is nowhere near over, with Israel having planned out 14 days of operations, a senior Israeli official said.
The likely duration of the campaign fits with analysts' expectations that a single wave of strikes wouldn't be able to do enough damage to Iran's nuclear program and Israel's comprehensive approach of attacking Iran's facilities, leadership and arsenal at the same time to limit the possibility of a retaliatory strike.
The pattern is similar to the one Israel deployed against Lebanese militia and Iranian ally Hezbollah—decapitating its leadership, degrading its arsenal and pushing it to a settlement. The current conflict could similarly end in a negotiated deal, the official said.
Iran has only two viable ways to respond to the attack. One is, as Scott Ritter lays out, an overwhelming destructive strike on Israel itself. This must be sufficiently hard for Israel that it will ask the U.S. to negotiate an end to the war. This would however risk nuclear strikes by Israel on Iran.
Another potential is to retaliated against the power behind Israel which conspired with it to launch the attack. There are U.S. targets in the Middle East which Iran could easily strike at. But the response from the U.S. would be an air and missile war that would overwhelm any defenses Iran has left.
A more reasonable attack on the U.S. will target its economy. Iran can stop its production of oil. It has various means to stop oil and gas production in U.S. allied countries situated in its neighborhood. It can close down the Strait of Hormuz through which 25% of the global hydrocarbon productions is flowing. There is the little the U.S. could do to prevent Iran from sustaining such a blockade.
As I have stated previously:
Trump wants lower oil prices and freedom to pursue his domestic agenda.
A few month of oil prices above $200 per barrel would devastated the chances for Republicans to keep the House and the Senate. It would ruin Trump's presidency. The would turn the world against Israel. Trump would be forced to sue for peace with Iran.
There would be strong collateral damage in the global economy. Iran would be blamed for it. But everyone would also know that it was not Iran or its leader who started this.