While the US could prevent by threat or intervention directly (the carriers in the med could prevent any Sov airlift & the 6th Fleet seaborne intervention, that would require US & Soviet forces fighting straight out & very very bad possibilities. Assuming that the Syrians break through the Golan, and the Egyptians enter the Negev, there is really nothing the US can do conventionally against the Arabs. Air strikes on supply lines in Syria, Sinai, but given that the Arab forces will be "hugging" the Israelis and going through inhabited areas, US a/c off carriers simply can't do CAS - there are no ground controllers. However many Marines there are with the MEU in the med simply are not enough to make a difference.
Bottom line is that if facing probable defeat (=destruction of Israel) the Israelis will do whatever they have to to prevent it. Target selection can be argued about, but use of nukes WILL happen.
Bottom line is that if facing probable defeat (=destruction of Israel) the Israelis will do whatever they have to to prevent it. Target selection can be argued about, but use of nukes WILL happen.