This is not quite accurate. Rather it is possible that it is not a sin. It is also possible that it is a sin, and even possible that it could be a mortal sin, depending on one’s intent and level of understanding. It is my belief that many Catholics will find their way to Hell over the issue of abortion. Many more will spend time in the metaphoric sea of Purgatory with millions of metaphoric millstones.
Remember that the instruction from the Church (on not even you can deny) is that we have the absolute moral responsibility to mold our own conscience, then vote accordingly. Failure to do the first will not exonerate us on the second, though it does mitigate it.
Second, we are told in the preamble that we are citizen’s of two countries, and America is the one we are only passing through. Our duty lies ultimately to the Kingdom of God. I admire the truly good Catholic Democrats here (and that is** not** an oxymoron, you guys). I thinks it important, as we have had this party for the whole history of our country, that we not give up on it. Likewise, I respect the Republicans that can do this, though I admit to being somewhat burned out with that struggle personally. In the end, it is more important we vote morally than that we vote partisan. We can not do that if we are not first ourselves moral. It is this that Catholics lack. When we become more saintly, we will become more unified.