When should a pastor call out another pastor as a heretic?

Mike argues it depends on whether the congregation is being influenced by the pastor in question. He gives Rob Bell as an example: when Bell embraced heresy, Mike did not address it with his congregation because they were unaware of Bell. Had they been reading his books, Mike would have spoken up. The duty is to protect the flock. The severity of the heresy and its impact on the congregation are both factors.