In mid-November, conservative news outlets posted multiple videos of Jonathan Gruber, an MIT health economist who worked on Romneycare and Obamacare, crediting the "stupidity" of American voters as one reason that the health law passed. The videos were not flattering for Gruber; Democrats have moved quickly to distance themselves. And, perhaps more consequentially, they have breathed new life into the Obamacare opposition effort. Today, the House Oversight Committee is holding a hearing with Gruber titled "Examining Obamacare Transparency Failures." ... Here'a a quick guide to who Jonathan Gruber is, why he's at the center of this controversy, and what it...