This is, of course, speculative, but makes a lot of sense given make up of the US government.
http://www.zmag.org/content/showarticle.cfm?SectionID=67&ItemID=10649<edit>
A US attack on Iran has been predicted by analysts for several years. The US policy vis-a-vis Iran is clearly directed towards confrontation rather than accommodation. There are many reasons for the US to attack Iran, including the control of energy resources, suppression of a regional power opposite to US and Israeli interests, etc. However I have argued for many months that the key reason for the US to seek a military confrontation with Iran is that it will "force" the US to cross the nuclear threshold and use low yield nuclear weapons against Iranian installations. And this is seen as essential to further US geopolitical goals.
The United States used nuclear weapons against Japan not because it had to. It did so to demonstrate to the world that it was in possession of a new weapon that packed the destructive power of thousands of bombing missions into a single one. To tell the rest of the world, beware.
Since then, it has spent over 5 trillion dollars in building up its nuclear arsenal, but nuclear weapons have become "unusable" after 60 years of non-use. America has achieved nuclear primacy but it is useless, until it shows that nuclear weapons are usable again.
Everything has been put in place. The US is likely to have obtained classified "intelligence" concerning hidden Iranian chemical and biological underground facilities. Low yield B61-11 nuclear bunker busters must have been deployed, just in case "surprising military developments" give rise to "military necessity". Once Iran is drawn into a conflict and shoots a single missile against Israel or US forces in the region, the US administration will argue that the next Iranian missile could carry chemical or biological warheads and cause untold casualties among Americans, Iraqis or Israelis. A low yield nuclear bunker buster will be touted as the most "humane" way to prevent further loss of life.
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Similarly, much evidence indicates that a deliberate project, shrouded in secrecy, exists today that will culminate in the nuking of Iran, to "save lives". Many are privy to parts of the plan, as Seymour Hersh revealed, only a few know the plan in its entirety. Low-yield nuclear bunker busters will be used, untested but as reliable as the untested "Little Boy" that leveled Hiroshima. Americans will buy the "military necessity" argument because it will be true: American troops in Iraq will be sitting ducks facing Iranian missiles, with or without WMD warheads.
After the US uses nuclear weapons again, it will have established the usability of its nuclear arsenal against non-nuclear countries. It will be possible to wage war "on the cheap", saving many American lives in future conflicts. "Support the troops" is the one thing all Americans, no matter how diverse their views are, agree on.
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