In her history, has the Catholic Church ever declared any group that identified itself Christian as not Christian?
The answer should start with the most recent declarations if any exist.
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I know for a fact that the Catholic Church does not recognize those who do not baptize in the proper form and matter as Christians. Thus the Catholic Church does not recognize the validity of groups such as Mormons or Jehovahs Witness (although I don't think the Jehovah's witness consider themselves Christian to begin with)
The Catechism of the Catholic Church states:
The Church knows that she is joined in many ways to the baptized who are honored by the name of Christian, but do not profess the Catholic faith in its entirety or have not preserved unity or communion under the successor of Peter. Those who believe in Christ and have been properly baptized are put in a certain, although imperfect, communion with the Catholic Church. With the Orthodox churches, this communion is so profound that it lacks little to attain the fullness that would permit a common celebration of the Lord’s Eucharist. (CCC 838)
There is also this from Catholic Answers ("What is the relationship between the Church and baptized Protestants?"):
Validly baptized Protestants are regarded as true Christian brothers and sisters who are in imperfect relationship with the Church. The nature of the imperfections is as varied as Protestantism itself. The idea at work here is that the faith is an incarnational thing, not just a "spiritual" (disembodied) thing—just like Jesus himself. Thus, it is possible to be out of union with the Church "bodily" (structurally, sacramentally, liturgically), yet still have a spiritual unity with the Church. Likewise, it is possible to be "bodily" united to the Church yet cease to be in communion with her spiritually (as an apostate Catholic is if he keeps going to Communion yet rejects the creed or continues unrepentant in grave sin). The latter form of disunity with Church is more serious than the former.