Here’s a link to a recent Christianity Today essay, “The New (Evangelical) Mainline.”
The contention is that evangelicalism is replacing mainline protestantism as the “big middle” (my term) of American Christianity. Denominationalism is in decline, along with the mainline denominations (add to that the Southern Baptists as well—a very large evangelical denomination), according to recent surveys that have enjoyed media attention (ARIS, Pew Center here and, more broadly, here). This includes my denomination, United Methodism, which has its done its own data collection and interpretation work confirming our numerical decline. Parenthetically, some areas (annual conferences) within American United Methodism seem to be responding to the data with more vigor and creativity than others.
One of the dynamics at work here, in addition to the non-denominational church movement/phenomenon (bible church, community church, etc), is the way that the major mainline protestant denominations—United Methodists, Episcopal Church of America, Evangelical Lutheran Church in America, United Church of Christ, Presbyterian Church (USA), Christian Church (Disciples of Christ), and perhaps also the American Baptists—include persons who would identify strongly with liberal Protestantism, but also those would would identify strongly with evangelicalism.
The question that comes to my mind is: What do we make of the evangelicals and evangelicalism we find within the mainline Protestant denominations? What will the future be for them/it?
Guy M Williams 
I think the answer to your question depends on whether local churches “make room” for evangelicals. What is the theological slant of each church?
Even more interesting, wouldn’t we also have to say that the original roots of the mainlines are more closely related to the evangelical DNA than the liberal DNA? This is what confuses me even more.