Iran is astutely denying oil to those European countries which import the least from them. It is the European countries of the Mediterranean, namely Greece and Italy, which import the most oil from Iran. There is already a wedge with France and Germany on one side on the Euro crises and Greece and Italy as well as others on the other side. Iran hopes to leverage this wedge with its tactically placed sanctions. That may or may not succeed.
I believe that Obama will go to war before the elections but as close to the elections as possible. He can bet that the Republicans will be pushing for war along with bellicose Democrats and the Israel lobby. If he launches the war too early and it does not go well, then the Republicans can present him as a poor commander-in-chief. However, if he times his war just right, he can take the bellicose wind right out of the Republicans' sail. I predict war in late September or early October unless some other variable comes into play.