Double effect, Lad. It is licit to vote for a bad candidate to prevent a worse candidate.
You clearly have absolutely no idea what you're talking about. Double-effect does not mean voting "to prevent a worse candidate". What you articulate is NOT double-effect but lesser evil.
That's like saying that it's OK to remove a baby in an ectopic pregnancy in order to prevent the greater evil of having both the mother and the baby die. That is NOT CATHOLIC. You are performing an operation in order to save the life of the mother (note, you are not killing a baby), the unintended consequence of which would be the death of the baby. It must be an unintended SIDE-EFFECT of something that's a good (saving the life of the mother), which outweighs the harm of the double-effect.
In double-effect ...
1) the action itself must be good -- I am saving the life of the mother
2) you must only intend the good part (and not the secondary effect) -- I am not intending to kill the baby
3) the good effect cannot arise from the bad effect (must be the other way around) -- I am not directly killing the baby but removing a damaged organ (there are ways that this procedure can be done and ways it cannot be done in order to comply with this)
4) the bad effect cannot be disproportionate with the bad effect -- (I cannot remove the organ simply to help the mother's mental state for example)
So let's apply this to voting.
I am voting for a candidate who promises to appoint Pro Life justices to the Supreme Court (assuming you can believe any of these liars). But this candidate wants to attack some country unjustly, resulting in the deaths of many innocents. By voting for this candidate, I intend to help put into power someone who might change the plight of the unborn and not someone who would attacks innocents in an unjust war. In that case, the latter would be an unintended secondary effect (the double effect). Here one can argue regarding the proportionality (the question of whether such a person's appointments will in fact make any difference vs. the probability that this person would kill innocents in an unjust war).
But to vote for a candidate to prevent a worse candidate from arising is "lesser evil" thinking and is not Catholic. And I vehemently disagree with those theologians who claim otherwise. So the candidate you vote for must in fact be a good. You cannot vote for a bad candidate in order to prevent a worse candidate.
So let's apply that to the case I cited earlier, where you have one candidate who's for abortion in the first trimester and another who's for abortion on demand throughout the pregnancy (even to the point of partial birth). You cannot vote for the first trimester guy based on double-effect, because he's not a good candidate. You cannot do it even in order to prevent a worse guy from getting into office. You're doing a BAD in order to prevent a GREATER BAD. And here's the difference that most of you fail to understand. According to "lesser evil" thinking, then yes you could vote for the first trimester guy. But according to Catholic double effect, you cannot. Now, if the first trimester guy stated that he intended to work for making abortion illegal after the first trimester, then you COULD vote for the guy ... based on the good of his wanting to make abortion illegal under those conditions. But there MUST BE SOMETHING GOOD in the candidate that you are intending to vote for (without the relativism of comparing him to another candidate).
In the case I just mentioned,
1) you are intending a positive good (wanting abortion illegal after the first trimester)
2) do not intend the bad (wanting to keep it legal in the first trimester)
3) the bad part doesn't come directly from the good part
4) and the bad is not out of proportion with the good