“One may not do evil so that good may result from it.” (Catechism of the Catholic Church, §1756). 
It has become proverbial in the United States that we choose between the lesser of two evils at election time. While each candidate for a public office has his partisans, it seems that there is a vast number of voters who feel a compulsion each election cycle to select the candidate they feel will do the least damage and bring about the least amount of evil.
As melancholy as the situation is, there is logic to voting in that manner. It seems to be of common sense that lesser evils are to be avoided to greater ones. Interests and issues can be ranked according to priority for each individual voter, and it seems plausible that, in a democracy where compromise must happen, each voter should vote in accordance with that ranking.
This works well if a voter perceives that there is only one issue where true good and evil are at stake, and that the rest of the issues, while susceptible of a preference, are morally neutral. For example, a pro-life voter, voting in a local election, may vote for a particular candidate because he knows that the candidate will oppose the construction of an abortion clinic in the area, even if that candidate is in favor of widening a particular street and the voter opposes it.
But there are many elections where a voter may feel that there is more than one moral issue at stake. For example, the voter may be pro-life as to abortion, but may also believe that unjust war, which also takes human life, is equally evil. In choosing between two candidates he may legitimately believe that the promotion of abortion is more likely if one candidate is elected, and the prosecution of an unjust war is more likely if the other candidate wins the election. Confronted with such a political landscape, this voter is faced with a conundrum.
A priority ranking in this situation would be difficult for one who wasn’t a party loyalist. Voting is a choice, a voluntary act, and we are responsible for the foreseeable outcomes of whatever we do deliberately. If one decides to assist someone who will unjustly kill hundreds of thousands of people, he is not exonerated because he did that rather than aid in the killing of millions where he could have chosen to do neither.
A vote for a particular candidate is direct assistance to that candidate to be placed in a position of power so as to implement the policies that he announces beforehand. Since a voter has a choice whether he will vote at all, he is not absolved of the evil that his chosen candidate commits, and has announced beforehand, because he did not vote for the candidate who would have committed the evil in a manner that would have impacted more people. This is because every individual human person is to be considered an end in himself; no human being is to be thought of as expendable.
The attempt to vote for the lesser of two evils involves both despair and moral compromise. Politics should not be allowed to be so soul-damaging. If voters stop engaging in the practice, and simply stop voting for candidates who they feel will do evil on any level, the two major political parties may be compelled to seek out those voters with changes in both their positions and their candidate nominations. That effort could be enhanced if voters of like mind organized for the purpose of identifying the position requirements of candidates who would obtain their votes.
The manner in which this could be done would be the formation of a visible voting bloc. Thinking particularly of Catholic social teaching, like minded voters could organize and agree that they would vote for no candidate who didn’t subscribe to all of the stated positions of the bloc on such matters as abortion, just war, the rights of labor unions, and the preferential option for the poor. With sufficient numbers and visibility, such a bloc could have a significant impact on the positions candidates take during campaigns, as well as the actions they take once they are in office.
If a third political party emerges that is in accord with the voting bloc, both the bloc and the party could work together to achieve mutually favorable outcomes. In the United States, third parties can serve as spoilers in some elections, a result that the major parties want to avoid. Should neither of the major parties decide to field a candidate acceptable to the bloc in a given election, bloc members could cast all of their votes for the third party candidate, with results that could impact the success of one or the other of the major party candidates. What’s more, if membership in the voting bloc reached sufficient levels, it could give the third party a credible basis for making challenges in its own right. That hasn’t happened in the United States since before the Civil War, but the major parties may assume that the historical process is stagnant to their peril.
For Christian Democrats, that is, for those who support Catholic social teaching in its entirety, what has been outlined here may be the only way that like minded candidates will emerge as competitive. Clearly, the major parties will require more incentive than they have now if they are to adopt Christian Democratic positions completely. What’s more, a movement of this kind can only be successful if each Christian Democrat agrees to vote only in accord with his conscience—all of it.