The “Church(es) of Christ” and the “Christian Church (Disciples of Christ)” are two separate denominations, however both are descended from the Barton Stone & William Campbell restoration movement in the early 1800s.
A center point in the origin of the Disciples of Christ was over one having to be an official church member of a denomination or congregation rather than being a baptized Christian to partake in communion.
Here is the history of the DoC from its website: https://disciples.org/our-identity/history-of-the-disciples/
See also the Wikipedia entry: https://en.wikipedia.org/wiki/Christian_Church_(Disciples_of_Christ)
Thanks for the ping and the DoC links.
The decline is sad news for DoC members.