Bangladesh, Sept. 16 -- As the United States prepares to complete its military withdrawal from Iraq, Baghdad is approaching a sovereignty deadline it is unlikely to meet. The real obstacle is not logistics or legislation, but Iran's determination to preserve the armed networks that have become central to its influence over Iraq.

September 30 is supposed to mark a historic moment for Iraq. On that date, the United States is expected to complete its final military withdrawal from the country, more than two decades after the invasion that toppled Saddam Hussein and transformed the region.

Baghdad has presented the occasion as a kind of "sovereignty day"-a moment when the Iraqi state is supposed to demonstrate that it alone has authority o...