Iran and al-Qaida appear poised to fill the power vacuum created by the U.S. decision to withdraw remaining U.S. troops from Iraq by Dec. 31. President Obama announced that the soldiers will depart by then, leaving behind a small contingent to guard the U.S. Embassy.

The American departure sets the stage for renewed efforts by Tehran and jihadist groups to expand their power inside Iraq, potentially reversing many of the security gains made by U.S. and Iraqi forces during the past four years.

A few days after the withdrawal announcement, the Justice Department provided a new reminder of the destructive role that Iran has been playing in Iraq. DOJ announced the indictment of five people and four of their companies for smuggling U.S.-made electronic components into Iran.

Some of the parts have been used in the remote controls of improvised explosive devices (IEDs) seized by U.S. forces from Iraqi terrorists. From 2001-07, DOJ said, 60 percent of all American casualties in Iraq have been caused by the bombs, and the most deadly, sophisticated ones are produced in Iran.

The Obama administration had sought to keep several thousand troops in Iraq in non-combat and advisory roles. But after Washington and Baghdad reached an impasse over legal protections for the remaining troops, the president decided to withdraw all forces by the end of the year.

"Now we're going to have zero, which means there won't be forces to help maintain checkpoints between Kurds and Arabs," said Anthony Cordesman of the Center for Strategic and International Studies. "There are not going to be specialized forces to help the Iraqis deal with the kinds of terrorism and insurgent groups they have. We're not going to have any clear contingency basing structure that will allow us to rapidly deploy if Iraq faced a threat from Iran."

Shiite terrorist organizations began stepping up attacks already this year, with more than 40,000 troops still in Iraq, wrote security analysts Frederick Kagan and Kimberly Kagan. This included IED and rocket strikes targeting Iraqi security forces and American troops "using technologies that they had tried unsuccessfully to field in 2008 but have since perfected."

Meanwhile, Thomas Joscelyn of the Foundation for the Defense of Democracies has just published a disturbing new report on Ansar al-Islam, an al-Qaida-affiliated group with a history of collaboration with Iran. Read the article here.