According to the New Yorker:
"This summer, the White House, pushed by the office of Vice-President Dick Cheney, requested that the Joint Chiefs of Staff redraw long-standing plans for a possible attack on Iran, according to former officials and government consultants. The focus of the plans had been a broad bombing attack, with targets including Iran’s known and suspected nuclear facilities and other military and infrastructure sites. Now the emphasis is on “surgical” strikes on Revolutionary Guard Corps facilities in Tehran and elsewhere, which, the Administration claims, have been the source of attacks on Americans in Iraq. What had been presented primarily as a counter-proliferation mission has been reconceived as counterterrorism.
The shift in targeting reflects three developments. First, the President and his senior advisers have concluded that their campaign to convince the American public that Iran poses an imminent nuclear threat has failed (unlike a similar campaign before the Iraq war), and that as a result there is not enough popular support for a major bombing campaign. The second development is that the White House has come to terms, in private, with the general consensus of the American intelligence community that Iran is at least five years away from obtaining a bomb. And, finally, there has been a growing recognition in Washington and throughout the Middle East that Iran is emerging as the geopolitical winner of the war in Iraq."