Render unto Caesar the things that are Caesar's and unto God the things that are God's.
You are making a false idol of government. No one has any obligation to vote. Not even when it is Ronald Reagan vs. Jimmuh Peanut or Ronald Reagan vs. Walter Mondale much less when it is Myth Romney vs. Obozo or John Whackobird McCain vs. Obozo.
Bishop Tobin is the Ordinary of the Diocese of Providence, Rhode Island. His letter to a Rhode Island Catholic voter, republished, I believe, in the diocesan newspaper is the Church document you seek.
Pilate was a pagan and a Roman governor. He gets a bad rap in history when the historians do not stand in his shoes. It was not every Tom, Dick and Julius who became a Roman governor. One got one year to rape, loot and pillage one's domain as governor to pile up money to support one's family during the ensuing six years working as a bureaucrat at Rome without pay. One also, at all costs, had to keep the emperor's peace while being governor. Pilate was faced with a mob of about 300 troublemakers organized by Annas and Caiaphas, masters of the Temple, demanding that Jesus be crucified. Pilate sent Christ to Herod Agrippa in the hope of being relieved of the decision as to Jesus Christ by a merciful decision. No such luck! Pilate had christ brought forward with Barrabas, a genuine notorioso, and assumed that the crows would choose Jesus for pardon but, again, no such luck! Was Pilate a hero? Hell no! Was he some sort of horrible criminal from a pagan Roman point of view? Again, no!
John the Evangelist, then about fifteen years old, was certainly the only one of the Twelve to be at the crucifixion. The Romans would have had no way of knowing John's stature in the Faith and would have regarded him as a young fellow present to support Mary.
If there are no candidates for an office other than bad candidates, one ought not vote among the bad candidates. Do that too often and you will soon vote for a Myth Romney over Obozo because it is better to protect Muffie's trust fund than not even if both candidates will kill babies, support "gay""marriage," grab guns, etc., etc., etc., ad infinitum ad nauseam. Caesar has no right to expect us to vote for Caesar's candidates.