Time to Leave
So the question isn't whether things will be ugly after American forces leave Iraq. They probably will. The question, instead, is whether it makes sense to keep the war going for another year or two, which is all the time we realistically have.
Pessimists think that Iraq will fall into chaos whenever we leave. If so, we're better off leaving sooner rather than later. As a Marine officer quoted by James Fallows in the current Atlantic Monthly puts it, "We can lose in Iraq and destroy our Army, or we can just lose."
And there's a good case to be made that our departure will actually improve matters. As Mr. Murtha pointed out in his speech, the insurgency derives much of its support from the perception that it's resisting a foreign occupier. Once we're gone, the odds are that Iraqis, who don't have a tradition of religious extremism, will turn on fanatical foreigners like Zarqawi.
The only way to justify staying in Iraq is to make the case that stretching the U.S. army to its breaking point will buy time for something good to happen. I don't think you can make that case convincingly. So Mr. Murtha is right: it's time to leave.