"Red Letter Christians are a group of liberal Christians whose desire is to counter the political influence of conservative Christians. In the past thirty years, the voice of evangelical Christianity has been fairly prominent in the political process, much to the chagrin of secularists, non-evangelicals, and liberal Christians. As conservative Christians networked in such groups as the Moral Majority, the Christian Coalition, and American Values, popular figures within liberal Christianity began to feel disenfranchised. They deemed their faith to have been “hijacked” by the religious right.
Framers of the Red Letter movement include Jim Wallis, founder of
Sojourners magazine; Shane Claiborne, an activist and leader in the
New Monasticism movement; Richard Rohr, a well-known Catholic writer; Brian McLaren, an
emergent church leader; and Tony Campolo, a popular speaker and author of
Red Letter Christians: a Citizen’s Guide to Faith and Politics. These men desired to counter the voice of evangelicalism in the political world."
More info here:
What are Red Letter Christians? | GotQuestions.org