For the past several months, the Israelis have been threatening to attack Iranian nuclear sites as the United States has pursued a complex policy of avoiding complete opposition to such strikes while making clear it doesn't feel such strikes are necessary. At the same time, the United States has carried out maneuvers meant to demonstrate its ability to prevent the Iranian counter to an attack -- namely blocking the Strait of Hormuz. While these maneuvers were under way, U.S. Secretary of State Hillary Clinton said no "redline" exists that once crossed by Iran would compel an attack on Iran's nuclear facilities. The Israeli government has long contended that Tehran eventually will reach the point where it will be too costly for outsiders to stop the Iranian nuclear program.
The Israeli and American positions are intimately connected, but the precise nature of the connection is less clear. Israel publicly casts itself as eager to strike Iran but restrained by the United States, though unable to guarantee it will respect American wishes if Israel sees an existential threat emanating from Iran. The United States publicly decries Iran as a threat to Israel and to other countries in the region, particularly Saudi Arabia, but expresses reservations about military action out of fears that Iran would respond to a strike by destabilizing the region and because it does not believe the Iranian nuclear program is as advanced as the Israelis say it is.