He used to do a right/left debates show with Steve Brown. I don't agree with Tony, but I've never seen him unhing while debating conservatives. He is thoughtful and reasonable--and a brother in Christ...who is not a Republican, Democrat, or American for that matter!
I personal suspect Jim Wallis and Tony Campolo are theological liberals (because of their abortion stance: note that they don't oppose others to do abortions, and they believe in homosexuality not a sin), but I do know genuine Christians who lean left on defence/foreign affairs/WOT, economic systems and social welfare. In fact, they will be the majority among non-Western Christians.
I would consider them to be diametric opposite to Ayn Rand objectivists. We do have Randists on this site. Search for FRer Oztrich Boy for instance.