Christians ought to know their opponents. In recent years, one of those opponents has been Marcus Borg, now deceased, formerly professor of religion and culture at Oregon State University. Borg’s life was a constant journey toward the theological Left. I heard him lecture when he was in Minneapolis in 2011. He was an engaging and fascinating speaker whose views were well beyond the liberal mainstream.
If you want a nice little introduction to Borg, here is a piece in the Christian Century by Thomas G. Long. It’s a good summary with a focus on Borg’s last contribution.