There is no unique situation provided by this election cycle. Voting one’s conscience is essential in every election cycle. The intrinsically evil acts of abortion, euthanasia, embryonic stem cell research, as well as the duty to safeguard the biblical definition of marriage, have all be relevant for several decades. There have been no authentically Catholic presidential candidates since the abortion issue arose with Roe v. Wade in 1973. In my lifetime, there has been no evidence that case law on abortion will be overturned in the foreseeable future. Much time and money has been wasted on chasing the phantasm of a “pro-life president.”
If, in obedience to God, a Catholic chooses to make a particular choice not to cast any votes, he or she would need to demonstrate that God so instructs. So far, I have not seen anyone attempt to satisfy this requirement.