Twitter CEO Dick Costolo says the company has to bridge the gap between the brand's global awareness and user engagement. Ethan Miller/Getty Images hide caption

itoggle caption Ethan Miller/Getty Images

Stephen Colbert responded to criticism about a tweet about his show from his TV network Monday, saying he would dismantle the imaginary foundation that created the stir. Comedy Central hide caption

itoggle caption Comedy Central

GOP Sen. John McCain greets well-wishers as he arrives to visit a pro-European Union rally in Independence Square in Kiev, Ukraine, on Dec. 15. Strong criticism and trips like this landed the Arizona senator on Russia's travel blacklist. Sergei Chuzavkov/ASSOCIATED PRESS hide caption

itoggle caption Sergei Chuzavkov/ASSOCIATED PRESS