In this election as in past elections many people of principle get into disagreements about whether it is right to vote for the “lesser of two evil” choices for an office like the President. Many Christians will say things like “Pray as if everything depends on God, but act as if everything depends on you.” This gets interpreted as pray that God will bring the best outcome from my point of view and act to get that same desired end. The problem with this reasoning relates to “my point of view” and the acts that follow.
The outcome is always in God’s hands. This is clear to anyone with even the most limited view of God’s providence. God has also given us His Word which tells us how to act and which speaks to all of life. We are to do the right thing always and I don’t see where this includes “doing whatever it takes to get the desired end.” Even if the end were right (assuming that eliminating one evil at the expense of many others can ever be right), that doesn’t mean that you can throw out the rest of your principles.
Just because a candidate is pro-life doesn’t mean he is the right choice (is he moral in other areas?). There should be other factors in consideration. Anyone can win that God wants to win and the candidates God doesn’t want to win won’t no matter how many Christians vote for him “because he can win.” I am going to vote for Chuck Baldwin of the Constitution Party. I admit that he probably won’t win which many will be too quick to point out (it won’t be my vote causing him not to win). Too many will say that I am wasting my vote. It may not seem unprofitable to many, but I cannot give my approval to either Barack Obama or John McCain – neither of these are good candidates.
the Great Lands 
Admittedly, there are many, many issues that go into this question. But I have become increasingly convinced that voting by “principle” or “conscience” (or whatever you want to call it) is the most consistent way to vote for a postmillenialist. It’s easy to become way too shortsighted and place way too much stake in the next president. But it’s only four years! Perhaps, in God’s vast plan for history He intends on things getting a lot worse before putting things back together. He’s done that before. Maybe God even intends on the complete demise of the USA. He raises up one nation and puts down another. (It is extremely dangerous to link God’s kingdom with the USA.) But in the meantime, God’s people need to live (and vote) righteously.
As I said years ago in the link you cite, right now the candidates we have are exactly what we deserve. And it is largely the Church’s failures that have brought about this sad state of affairs. Thus, Christians’ focus shouldn’t be on the next president but on the cleansing of the Church. Only when she reforms and begins fulfilling her responsibilities to the world will we ever see improvement.