"The Bush Administration characterizes Iran as a 'profound threat to U.S. national security interests.' The Administration perception is generated primarily by Iran's nuclear program but is compounded by Iran's military assistance to armed groups in Iraq and Afghanistan and to the Palestinian group Hamas and Lebanese Hezbollah. The threat assessment of some other governments was lessened by the December 3, 2007 key judgements of a National Intelligence Estimate (NIE) that indicates that Iran is likely not on a drive to develop an actual nuclear weapon, although Administration officials say that this finding was not the main thrust of the NIE, which judged Iran to be continuing uranium enrichment. […]. To strengthen its diplomacy, the Administration has maintained a substantial naval presence in the Persian Gulf. The Administration has strongly denied widespread speculation that it plans military action against Iran, but has refused to rule it out if no other efforts to curb Iran's uranium enrichment program succeed. Some in the Administration believe that only a change of Iran's regime would end the threat posed by Iran, but the March 14, 2008 parliamentary elections in Iran do not suggest a critical mass in Iran for toppling President Mahmoud Ahmadinejad or the regime, more generally."
CRS Report for Congress, RL32048