The Vatican, like most overseas "concerns," has been following the dynamics of the US Presidential elections closely, and it's rather obvious that they want the side who espouses their beliefs--pro-life beliefs--most closely, to win. Choosing between the side whose Presidential candidate argued that even infants who survive an attempt to murder them in their mother's womb deserve to die; and the side not only whose Presidential candidate has adoted a physically disfigured orphan, but whose Vice Presidential candidate has brought a child that she knew to be developmentally disabled to life (and not had it murdered in the womb); is a no-brainer for the Vatican. I, as a Roman Catholic, fully agree with and support the Church's decision in this regard.
They know that since 1980, who wins the Catholic vote in the US wins the Presidency (2000 was the exception). They also know that there are still some Catholics in places like Ohio and Pennsylvania (and even Michigan) who still follow Church teachings in this regard, and whose Number One issue in the voting booth is abortion. That vote may be enough to overcome ACORN in those places.