Jack, I like the way you point out that we gave a binary problem here, with a two-party system. This has become an acute problem for Catholics, because many of us thought we could just be Republicans like rooting for a football team. We're not avid sports fans in our house, but we did have to adjust our loyalties when our daughter started going to USC, since my husband went to UCSF and had always rooted for Cal. At least we have to keep track of the score and have some sympathy for bad games.
The Iraq war has been a wake-up call for Catholics in America, I hope. Some of us even feel that prolife voters have been used for ill purposes. This war was condemned by Pope John Paul II forcefully and for specific reasons. It was a preemptive strike, therefore not defensive as required by just war theory. (Our attack on Afghanistan was not condemned because it was considered defensive.) And it could be foreseen that the outcome would be worse than the previous state. Also it put the fragile Christian population of the Middle East in jeopardy. We also went in on false pretenses. All this has been argued elsewhere, so I'm not going to belabor it. The stance of the next president on war will not only affect Iraq, but also our relationship with Iran, South Korea, Israel/Palestine etc. The repercussions are quite serious for the whole world and I believe as momentous as the life issues we face as a society. Still, as my husband points out, it could be safer to have a more hawkish president if the person was reasonable and if our strength was oriented toward peace.
The Church has a lot to say human matters in the world, and fortunately it is easier to find out these teachings and to educate ourselves than it was in the past. Arguably the pope has the best informed and most disinterested (or non self-interested) diplomatic corps in the world (see How the Vatican Works, my review on John Allen's book All the Pope's Men). But more than that, I believe there's a reason we didn't just get a rulebook in the Bible or a catechism to apply for ourselves, but instead we're given the presence of Christ in teachers guided by the Holy Spirit, because He did not leave us alone.