Lawrence O'Donnell, host of "The Last Word" on MSNBC, has been off the air. He joked with Rachel Maddow ahead of his absence. Here's what to know.

Lawrence O'Donnell hosts "The Last Word" on MSNBC. MSNBC host Lawrence O’Donnell has been absent from his nightly show “The Last Word” this week, prompting questions from viewers accustomed ...