I've got some strong opinions on the capital punishment issue too.
Fortunately, The Catechism of the Catholic Church, in its 1992 form, does not exclude the possibility that a state could justifiably use capital punishment in cases "of extreme gravity," but adds: "If bloodless means are sufficient to defend human lives against an aggressor and to protect public order and the safety of persons, public authority should limit itself to such means..." [#2266, 2267]
Capital Punishment has continuously been regarded as morally licit, for the vast majority of the history of Christianity, with some modern changes in thinking.
St. Thomas Aquinas sums up the thought of most Christian tradition on the subject,
"The life of certain pestiferous men is an impediment to the common good which is the concord of human society. Therefore, certain men must be removed by death from the society of men.... Therefore, the ruler of a state executes pestiferous men justly and sinlessly in order that the peace of the state may not be disrupted.... [However], the execution of the wicked is forbidden wherever it cannot be done with out danger to the good. Of course, this often happens when the wicked are not clearly distinguished from the good by their sins, or when the danger of the evil involving many good men in this ruin is feared" (Book III, ch. 146).
Clearly, the continual teaching of Christianity has been that Capital Punishment is not only necessary but also just and licit. I don't think there is any danger for the Catholic politician who expresses this traditional view.