1. The specter of al-Qaeda rising again in Iraq
Sunni extremists wreaked havoc in Iraq during the first years of the war, killing huge numbers of civilians and sowing chaos in the Shiite-majority country, but declined in 2007. This large, apparently well-executed attack on Abu Ghraib was another datapoint in the group's alarming resurgence, and by freeing experienced fighters and officers, a significant strategic success. The growth of al-Qaeda's reach anywhere is bad news, but the group's history in Iraq is so dark and the damage it has caused so severe that the increasingly real possibility of its return to prominence is bad, bad news. And not just bad news for Iraq -- al-Qaeda's ambitions are regional and, if it grows strong enough, perhaps global.
2. Rising threat to Iraq's stability
Al-Qaeda's goal in Iraq is, transparently, the destruction of the state. As the world learned in 2005 and 2006, when the country had the benefit of tens of thousands of U.S. troops to help promote security, very bad things happen when Iraq is destabilized. In the past, that's meant security devolving from the state to militias, sectarian fighting, whole communities internally displaced, instability in neighboring countries and a wider opening for extremists of all stripes to seek influence. That means better conditions for al-Qaeda and an increased ability to sow chaos elsewhere. Violence in Iraq is already rising rapidly, a trend likely to continue and even accelerate.
3. May further radicalize Syrian rebels
A deeply worrying trend in Syria has been the influx of jihadist rebel groups such as Jabhat al-Nusra, which are not just gaining territory but radicalizing the fragmented Syrian opposition. A number of the now-freed Iraqi prisoners -- hardened fighters and ideological extremists -- are widely expected to join that fight in Syria. Things were looking bad there, but the rise of extremists makes the likely outcomes even worse. It makes a possible rebel victory look much scarier -- how much territory would al-Qaeda control in a chaotic, post-Assad Syria? -- and could leave outside powers such as the United States and Saudi Arabia with fewer good options.
4. Hard-won U.S. successes reversed overnight
For all the very real mistakes and setbacks of the U.S.-led Iraq War, one success was a program to kill or capture large numbers of Sunni extremist leaders, including officers and fighters with the once-powerful al-Qaeda affiliate there. These are very bad people who did terrible things to Americans and to Iraqis, often civilians. The United States, regardless of how you might feel about its decision to invade Iraq in the first place, expended lots of resources and more than a few American lives to put these extremist fighters away. Now a number of them are back out, undoing years of hard American-led work in just a few hours. As if we needed it, it's yet another discouraging coda to a war with plenty of them.