The main goal of these articles is not to convince or dissuade people about voting for a particular candidate or party. It is to foster a better understanding of the principles being invoked because an improper use of these principles can have bad results.
"A small error in principle can lead to a big error in conclusion."
Doing something, even something good, for a bad reason is not something we should be willing to accept because that would be acting contrary to our nature as rational beings. Therefore, even if you continue to support a given candidate, it should not be because of a faulty application of the principles of reason.
Where the principle commonly called "the lesser of two evils" is used to decide between two choices, the principle of double-effect only applies to a single choice. It is the method used to determine if a particular choice can or cannot be made. Thus, we have seen questions like "can a Catholic vote for Trump/Hillary?" Some commentators have attempted to answer these types of questions pertaining to the upcoming election using the principle of double-effect, but I believe these attempts are a misapplication of the principle.
The principle of double-effect answers the question of whether or not a specific single act is permissible when it is known that the act will produce not only a good, but also a bad effect. In the context of the political election it is proposed that, because we know a candidate will do both good and bad things, double-effect applies to the question of whether or not we may vote for a specific candidate. However, I believe that this is a misunderstanding of the principle as it applies to the question at hand.
The principle of double-effect addresses the following question.
Given an act that that produces two effects, one good and one bad, can we do the act?
To determine whether or not a particular act is permissible, the principle of double-effect applies four conditions to the act and its effects to arrive at an answer. If all of the conditions are met, then the principle of double-effect applies and the act may be done. The conditions which must be met for double-effect to apply are these.
The act itself must be good, or at least indifferent.
Both effects must proceed immediately from the act.
Only the good effect may be intended.
There must be due proportion between the good and bad effects.
The first two conditions determine whether or not double-effect applies to a particular act. If not, the act must be examined in light of other principles of reason. The second two conditions answer the question of whether or not an act to which double-effect does apply may or may not be done.
A fairly common example of how the principle is legitimately applied is the question amputating a limb infected with gangrene. Amputating the infected limb will remove the threat to life, but it will also result in the loss of the limb. Can we amputate the limb?
First: The act is amputation of the limb. This act is indifferent because the goodness or badness of it depends on the end toward which it is directed.
Second: Both effects will proceed immediately from the act. The moment the act is performed, both the threat to life and the limb will be removed.
Third: We only desire the good effect. If we could remove the gangrene without doing harm, or with less harm, we would do so.
Fourth: The good of preserving life is greater than the evil of losing a limb.
From this we can see that the principle of double-effect applies to this case, and that the reasonable conclusion is that we may amputate the limb.
Those who attempt to apply this principle as an argument for casting your vote for candidate X seem to do so on the basis of campaign promises. Even though it is likely that X will do some things we consider bad, X has promised to do other things we believe are good. We believe there is due proportion between the good and the bad that X will likely do while in office. Therefore, they conclude, the principle of double-effect shows that we can vote for candidate X. I will explain two reasons why I believe double-effect just doesn't apply to the question of your vote. Note that I am only addressing the question of whether or not double-effect applies to the question of your vote, there are certainly other factors that do.
Double-effect applies specifically to "an act that produces two effects, one good and one bad." We are examining the effects of specific individual act, so the act in question must clearly be the cause of those effects. In the case of amputation, both effects are produced by the act of amputation - they are both unavoidable effects of the act and the act is clearly the cause of those effects. Can we say the same thing about your vote? Is your vote the cause of both the good and the bad that candidate X will do while in office? The answer is obviously no. You cast your vote based on various things like campaign promises and position statements, but your vote does not actually cause any of those things to actually occur. Whether candidate X keeps or breaks every campaign promise, whether X does exactly what you expect or the opposite of what you expect can not reasonably be attributed as an effect of your vote. It is an effect of the free will of the candidate while in office.
I know that some will argue that your vote is the cause of the candidate getting elected and therefore, by extension, it is the cause of what the candidate does in office. I maintain that double-effect still doesn't apply even if we accept the argument. The principle of double-effect states that both effects must proceed immediately from the act. This is clear in the case of amputation. Both effects are immediate. They happen simultaneously and there is no delay between the act as the cause and its effects. In regard to your vote, none of the effects can be considered to proceed immediately from your vote. Even if we were to say that the effects in question will take place over a period of time, they don't even start to happen when you cast your vote. The candidate won't even get sworn in for two months after you cast your vote. X could refuse to be sworn in or die before doing so. Amputation guarantees that both the limb and the disease will be removed. Your vote does not even guarantee that candidate X will win the election. Clearly, double-effect does not apply to the question of your vote.
In the end, as stated in the previous article, you must exercise your prudential judgement. Faced with the fact that the candidate is not ideal, is it prudential to vote for X rather than one of the several other available candidates? Is it prudential to (once again) compromise on what you really want and vote for X as a step toward a greater good to be more fully achieved in the future? There are many factors to consider for this important decision. I hope that these articles will help clarify the good and bad points some are making on the subject. These decisions are unfortunately difficult and complex. The principles of reason exist to assist us in understanding the factors that go into making a good decision. It does not help if our thinking gets muddled by the improper application of these principles, even if those doing it have the best intentions.