Nobel Prize-winning economist reacts to Trump's attacks on him and claim of 'BEST MARKET IN HISTOY'

After Nobel Prize-winning Economist Paul Krugman pointed out Donald Trump's policies were hurting the U.S. economy, Trump attacked him online calling Krugman a "Deranged BUM" in a social media post in which the president misspelled the word “history" and incorrectly claimed Krugman still works for The New York Times. MSNBC's Lawrence O'Donnell is joined by Paul Krugman.