as much as I understand the Israeli policy in general and the current government's in particular, I think it is a real option. it goes deep to the Israeli and Jewish psyche understanding and perceiving it as a real existential threat. Israel will do all efforts to convince US to tighten the sanctions, try to sabotage and to delay developments and progress but if eventually Iran will become a threshold nuclear military state, Israel will act to prevent it. nuclear Iran is a real strategic hell for Israel (and for the rest of the region and free world) and it cannot afford it. 

I think you might find very useful materials in the INSS web under the title of publications use search Iran - http://www.inss.org.il/index.aspx?id=4356&cx=009063389744424113161%3At4lmrae0b7w&cof=FORID%3A9&ie=UTF-8&q=IRAN&sa=Search&siteurl=www.inss.org.il%2Fsearchframe.aspx%3Flang%3Dltr&ref=www.inss.org.il%2F&ss=1032j353970j5  

To answer this question we should remember some facts: first Israel is fully dependent on U.S politically, both in the region and on the international scene. Now from the point of the realistic cost benefit logic, attacking Iran is neither profitable for U.S nor good for the whole region and U.S Arab allies in the Persian Gulf. U.S and Saudies as well as Israelies all want to contain Iran but all of them know that using military option will be a deadly strategic mistake. Iran differ greatly from Iraq or Afghanistan or Syria. World know this very well so since the end of the 8 year imposed war of Iraq against Iran, they have withdrawn military options and started a series of other measures;  economic and cultural and political. The current cold and furious anti White House rhetoric heard in Tel Aviv are just a part of a permanent scenario which is essential for both the Israel Lobbies in the Hill to remind the Pr and also for the Pr to remind them his power of Veto. nothing more.

he Israeli assumption is that once it attacks Iran the US will back it. I am not sure that this working assumption is detached from reality and even it is, there is always a good chance for misperceptions of the Israeli leadership regarding this assumption. On the other hand I think that the Israeli leadership still prefers increasing the sanctions in order to reach a better deal with Iran.

History does not repeat itself but men commit the same mistakes again and again.

In 1938 the world was at the edge of a new war. The horrors of the previous one (WWI 1914-1918) were still fresh in the Europeans' memories. Nobody wanted a new war and politicians feared to confront the new German supremacist effort lead by Hitler. So when he demanded from the British and French that they stay away from his army and let him occupy a portion of Czechoslovakia (the Sudetenland), the British and French representatives - Neville Chamberlain and Edouard Daladier - chickened and succumbed to Hitler's pressures. They believed having avoided a new war. Less then six months later Hitler occupied Czechoslovakia and another six months later invaded and occupied Poland. On September 3, 1939 World War Two begun. It cost the lives of about 60 million people.

Very similar are the circumstance now. The Europeans are dead afraid of the terrorist groups sponsored by Iran. The same applies to the US. Both, the European political leadership and the American one, will try by all means to avoid a confrontation with the Iranian government and are willing to deliver Israel on a silver plate in exchange of "peace" with an eventual new nuclear power that could become uncontrollable.

So consider this: as in 1939 when WWII started, Britain was a year later left alone and almost lost the war, so it is very likely that the same would happen to Israel (be left alone) if/when Iran would announce that it has the bomb. The difference is that Israel fights for its survival thus the answer to Jessica's question is that the possibility of a preemptive attack by Israel is very high and could result in World War Three. This is why the smartest thing the European and US leaderships could do would be to energetically say NO to Iran's nuclear program and, if necessary, apply the heaviest sanctions. By now, they should have learned from their ghastly mistake on September 28,1938 (date of the so-called Munich Pact).