This is a superior article in The American Conservative by an ex-CIA officer who lays out in stark terms the difficulties facing Israel if they were to go it alone and bomb Iran's nuclear infrastructure.

Basically, it comes down to geography, technology, and the cold calculations for success.

A couple of excerpts:

Let's assume that the Israelis opt for an attacking force of 50 fighters, one third of which would be designated for suppression of ground fire. The planes would be equipped with conformal fuel tanks built into the fuselages for extended range. They would also have auxiliary tanks that could be jettisoned when empty. Nevertheless, the attacking force would have to take off from Israeli airfields and then almost immediately refuel either over Israel or above the Mediterranean because fighters burn considerable fuel in getting off the ground. Refueling from Israel's twelve modified Boeing 707 and C-130 tankers would take some time even though a plane using a flying boom for refueling can top up in thirty seconds. It is the maneuvering and connecting to enable the refueling that takes considerably longer. Refueling all 50 planes will be a major task essential to the success of the mission and while the planes are in the air and forming up they will be detected by radar in Egypt and Lebanon, information that one must assume is likely to be shared with Iran.

[...]

There are three possible routes to Iran. One route to the south violates Saudi airspace and it is by no means certain that the very capable 80 plus F-15s of the Saudi Air Force would not scramble to intercept. The other is to the north over Syria, skirting the Turkish border. Syria is unlikely to be able to interfere much given its current troubles though it does possess some capable Russian made anti-aircraft missiles, but a Turkish response to possible airspace violations cannot be ruled out. The third and most likely option is to fly along Syria's southern border, avoiding Jordan, and then through Iraq, which has only limited air defense capabilities since the US military's departure at the end of 2011.

[...]

Assuming that the Israeli Air Force is able to carry out the refueling, fly successfully to Iran, suppress ground defenses, and carry out its bombing, it still has to return home, again flying over Iraq with every air force and air defense battery in the region on full alert. Depending on how much maneuvering was required while over Iran, some planes might well need to be refueled again which would mean deploying highly vulnerable tankers over Iraq or Jordan.

Is it really doable? It is - if Israel is prepared to accept big losses. Those bombers simply can't manuever in the air with those 5,000 lb bunker buster bombs and the extra fuel attached. Assuming Israel would be unable to completely supress air defenses, the bombers would be sitting ducks.

But that still doesn't solve the question of just how much Israel can degrade Iran's nuke program. Even if everything goes off without a hitch, it is doubtful that Israel would set back the Iranian program more than a year or two. That's from Israeli intelligence.

The aftermath would be extremely dangerous too. The potential for hundreds - perhaps thousands of Israeli civilians dying in Hezb'allah rocket attacks not to mention Iranian retaliation should be weighed against how much the IDF could degrade Iranian capabilities.

Is Netanyahu bluffing?

On balance, all of the above suggests that the frequently repeated threat by the Israeli leadership to attack Iran is not a serious plan to take out Iran's nuclear sites. It is more likely a long running disinformation operation to somehow convince the United States to do the job or a deliberate conditioning of the Israeli and US publics to be supportive if some incident can be arranged to trigger an armed conflict. If one believes the two presidential candidates based on what they said in Monday's debate, both have more-or-less conceded the point, agreeing that they would support militarily any Israeli attack on Iran. Whether Romney or Obama is actually willing to start a major new war in the Middle East is, of course, impossible to discern.

It just doesn't seem credible that the Israelis would go it alone.