Complex sentence: Dean is a contributor to financial news network CNBC, and also a frequent guest on sister network MSNBC in shows such as The Last Word with Lawrence O'Donnell and he has also guest hosted "Countdown with Keith Olbermann" and "The Rachel Maddow Show".
Split into simpler sentences: Dean is a contributor to financial news network CNBC, and also a frequent guest on sister network MSNBC in shows such as The Last Word with Lawrence O'Donnell. He has also guest hosted "Countdown with Keith Olbermann" and "The Rachel Maddow Show".