First and foremost is to not allow the reestablishment, if you will, of an extremist sanctuary that can export the kind of terror that ended up with terrorists taking down the World Trade Center and plowing into the Pentagon and a field in Pennsylvania. That's the point: We started this war because the Sept. 11 attack came from this area. And we do not fight alone, but with some 40 allies who share that view.

The progress in Iraq is still fragile. And it could still be reversed. Iraq still faces innumerable challenges, and they will be evident during what will likely be a difficult process as the newly elected Council of Representatives selects the next prime minister, president, and speaker of the council.

The Islamic State fighters in Mosul are dead men walking and I think they increasingly know it.

US Ambassador to Iraq Ryan Crocker and I have repeatedly sought to emphasize that the progress in Iraq is fragile and also, possibly, reversible.

Let's remember that the reason we are there is that we have vital interests in Afghanistan, hugely important national interests, as do the other countries involved.

I think no commander ever is going to come out and say, 'I'm confident that we can do this.

I just don't know whether it was all destroyed years ago - I mean, there's no question that there were chemical weapons years ago - whether they were destroyed right before the war, (or) whether they're still hidden.