The biggest threat to Israel's existence is not Jordan, Syria, Saudi Arabia, Palestinian terrorists, etc. -- it's internal conflict between its own various political and religious factions.
Just like in days of old. What will it take?
Sadly, that seems to be a problem inherent in all democracies . . .
However, I do think that after the Gaza pullout, any ensuing Palestinian violence will unify the Israelis. The appeasers will realize (even if it is temporary) that appeasement was ineffective and will realize (again, temporarily) that you cannot negotiate with terrorists.
I think we'll see Ehud Barak and Shimon Perez arm in arm with Netanyahu and Sharon, calling for retaliation. I have already heard Barak saying that was the next step if Abbas did not hold up his end of the bargain. And with the settlers out of there, they can blast the junk out of Gaza . . .