I'll leave the specific RC issues to you, good folks. Prof. Feuerherd correctly debunks the myth cherished by some of you (and expressed in some of the less charitable comments) that decline is solely the result of alleged wooly theology and adoption of current cultural values within mainline churches. He correctly points out that demographics is destiny.

Our congregations often trace their start to the early 19th century. Our members in all the mainline churches are and have always been overwhelmingly white. African-Americans left early to form their own unique churches. We have no great wave of European immigration to sustain us. Hispanics when Protestant at all lean evangelical/Pentecostal, but mostly RC. Asians have provided some small increase for us. Take away Hispanics, Filipinos and Vietnamese and where would you be? France and the low countries I suggest.