In August 2005, Vice President Dick Cheney ordered Strategic Command (STRATCOM) to prepare a plan "to be employed in response to another 9/11-type terrorist attack on the United States (including) large-scale air assault on Iran employing both conventional and tactical nuclear weapons … not conditional on Iran actually being involved in the act of terrorism directed against the United States."
Rep. Ron Paul from Texas, who is currently considering a presidential candidacy, expressed concern "that a contrived Gulf of Tonkin-type incident may occur to gain popular support for an attack on Iran."
If America invades Iran, the escalation of war would dwarf the current situation, where we are primarily fighting a minority Sunni insurgency. The Shiite government, which we have installed, armed and trained, is pro-Iranian. The Shiite militia leadership has promised its American-trained forces would attack America if it invades Iran. Iraq's new parliament is aligned with Tehran. It is dominated by the United Iraqi Alliance, which includes the Supreme Council on Islamic Revolution in Iraq (SCIRI), whose headquarters are in Iran. It also includes the Dawa Party, whose leadership visited Tehran in January 2006, and whose military engaged the U.S. Marines for three weeks at Najaf, in November 2004.
President Bush's intelligence on Iran's "here we go again" nuclear weapons program was obtained from a guerrilla group called the Mujahideen-e Khalq (MEK), translated "People's Mujahideen (fighting force)." MEK was created in 1965 under Soviet-sponsorship, by Marxist revolution ideology. MEK participated in attacks on the Shah of Iran, aligned itself with Khomeini, and participated in the Iran hostage-taking, before it was expelled from Iran. MEK was welcomed in Baghdad, participated in the Iran-Iraq war. Today, MEK is postured to benefit from a regime-change in Iran.
I don't see any reason for United States' presence in the Persian Gulf, except for escorts through the Strait of Hormuz; and I don't believe President Bush's non-corroborated intelligence.