Christopher H. Evans’ Liberalism without Illusions: Renewing an American Christian Tradition (2010) provides a brief history and qualified commendation of the American tradition of liberal Christianity. He discusses the roots of liberalism in the 19th century, its flowering in the Social Gospel movement, and its continuing diffusion and influence throughout the 20th century. As the title suggests, Evans is far from uncritical of the liberal tradition, but he thinks it still has much to contribute to the revitalization of mainline Protestantism. For example, Evans argues that contemporary liberal theology is too rooted in academia and too detached from congregational life and the living sources of Christian tradition. In particular, he says, liberalism needs to engage more constructively with contemporary evangelicalism; after all, many of the giants of liberal Christianity came out of the evangelical milieu of the late-19th and early-20th centuries. Liberal religion will probably remain a minority preference for the foreseeable future, but American still needs a theological tradition that engages critically and constructively with secular thought, responds to systemic social injustice, and promotes pluralism in theology.
Michael Langford’s The Tradition of Liberal Theology (2014) is less historical and more directly theological and philosophical than Evans’ book. It describes and defends a tradition of Christian thought stretching back to the 2nd century that emphasizes the compatibility of faith and reason, the goodness and rationality of God, theological pluralism, and a nonliteral approach to the Bible, among other elements. He sometimes calls this “liberal orthodoxy” to emphasize its commitment to central Christian doctrines like creation, incarnation, and Trinity. Langford identifies 13 historical figures whose thought contributed to this tradition and argues that it continues to be a viable approach to Christianity in the 21st century. In contrast to Evans’ more America-centric approach, Langford focuses on a particularly (though not uniquely) British tradition and emphasizes philosophical considerations more than social reform. But these books provide complementary rather than conflicting defenses of liberalism.
I wouldn’t identify myself as a full-blown theological liberal, but I think the tradition still has valuable contributions to make to the future of Christianity. These two books provide a good start for thinking about what those contributions might be.