Iran's regime, and their nuclear program, are the main existential threat to Israel today. Their missiles have the range, and an attack could be made from the sea as well, with a suicide civilian ship.
Even if non-nuclear, Iran's new operational proximity to Israel in Syria, could (will) allow them to fire a lot of rockets into the Golan, with some degree of deniability in the near future, if they are not driven out, or their regime changed.
The good news is that Iran is nothing like the chemical warfare specialist that Iraq was under Saddam. The bad news is that the Assad regime is modeled after Saddam's Iraqi Ba'ath Party, when it comes to their military's chemical warfare posture (the old Soviet model). Also, Russian capability could be purchased covertly from the Government, or more likely, from individuals with the knowledge, or from elements withing Iraq.
So shorter flight time Scud/Shahab-1 with chemical warheads, or Fateh-110s could possibly be (have been) smuggled forward by Iran into Syria or Lebanon, which could pop chemical warheads into Haifa or Tel Aviv from Syria. Hizbollah has received the Fateh-110s before.
The Fateh-110 is the new Scud-like threat (SRBM) to Israel. They are solid fuel missiles, small enough to be smuggled in standard 40 foot shipping containers, with a somewhat smaller payload (500-650 kg, instead of 1,000).
Regime change in Iran is really the best protection.
