The answer to your question, "does it serve America’s interests to risk further entanglement in an internal power struggle among Iraq’s Shiites?" is not yet known. That is the point that needs to be understood by the American people. The answer to the question cannot be known if America pulls out, or so much as sends a signal of intent to do so, because it will create pressures and incentives to get out before the full interests of America, and with it the Western world and not least Iraq and the Middle East as a whole, is truly known. That is the position of responsibilty that is a burden on the shoulders of the American people - like it or not.