Since 2003, Iran had been pumping millions of dollars per month into Iraq in a bid to become a player on Iraq's political stage. With the emergence of the Iranian-backed Shia parties like Dawa and SCIRI as the most powerful forces in Iraq's government, Iran can rest assured that it has played its cards right. While the United States could deal with one enemy, it now has to deal with factions within Shia parties taking up arms and forming new policies with absolute disregard for the government and rule of law. This is evident in Basra, the second largest city in Iraq, where religious leaders and militias loyal to Shia political groups are the de facto rulers, imposing strict observance of Islamic law. It is also apparent that the Iraqi security forces and army are heavily infiltrated by militia members serving their political leaders rather than the citizens of the country.
Iranian politics is spreading to Iraq, and its most visible form is the public enforcement of strict Islamic lifestyle rules. Islamic radical factions within the Iranian government are sending millions of dollars a month to Shia political parties in southern Iraq. There, the money pays gunmen serving pro-Iranian Shia militias. Following the lead of their fellow Islamic radicals across the border, the gunmen defy Iraqi police and bully Iraqis in their area to observe Iranian lifestyle rules. This means beards for men and burkas for women. No alcohol or un-Islamic entertainments are allowed either. This means shopkeepers serving alcohol, videos or musical recordings are forced to stop, or risk physical attack. So far, complaints to the government have gone unanswered. The local officials don't want to start another war, and pass on the complaints to Baghdad. British troops have remained neutral. When British soldiers did try to interfere, they were attacked. This resulted in Iraqi and British casualties. In response, the British backed off, especially after the local government sided with the militias. The national government is trying to negotiate a disarmament of all the militias in the south. This will require moving more troops and police to the south, but this cannot be done until the Sunni Arab militias in central Iraq are disarmed, or at least convinced to stop attacking government forces. Diplomatic pressure on Iran has failed, because Iranians admit that the trouble is being fomented by Iranian Islamic radicals that the government cannot control. Iran is run by a coalition of Islamic conservative groups. They stick together because they represent only about a third of the population, and know that openly feuding could lead to losing power. This coalition has stopped holding fair elections (by barring many opposition candidates from even running), and knows that the more radical factions are the ones, in the end, that can be relied on to use force against rebellious Iranians.
The Iranian radicals are also ignored as they allow Iraqi Sunni Arabs to use Iran for at least one terrorist training camp. Syria also does this, but Iraqi Sunni Arabs have long persecuted Iraqi Shia. But the Iranian Islamic radicals hate infidels so much, especially Americans, that they will tolerate this, Hatred makes strange bedfellows.
The U.S. knows a lot about the Iranian and Syrian training camps, but apparently feels that the diplomatic fallout from bombing two more Islamic countries is not worth the small impact this would have on counter-terrorist operations inside Iraq. Moreover, these camps are more properly a problem for the Iraqi government, which continues to badge Iran and Syria with complaints.