Bush is doing just that in Iraq.
It's fundamental justification was sound from the beginning and still is today. The war on terror, and the center of the storm is now in Iraq, and not here. Saddam's capacity to destroy his own people, his neighbors, and US through continued coordination with alQaida is GONE. And Iraq will be a democracy in the center of the darkest region in the world.
It was the RIGHT thing to do.
All of those are ex-post-facto justifications. None of them were our stated reason for going to war.
Again, the Iraq invasion really has not served our interests, even if it served those of Iraqis. There's absolutely no evidence that we've made ourselves safer from terrorism by going to Iraq.
If we'd spent that $300 billion on patrolling our borders, then we'd be safe from terrorists. As matters stand, anyone with the will to do it still can, Iraq invasion or no Iraq invasion.