Glenn Greenwald In their zeal for control over online speech, House Democrats are getting closer and closer to the constitutional line, if they have not already crossed it. For the third time in less than five months, the U.S. Congress has summoned the CEOs of social media companies to appear before them, with the explicit intent to pressure and coerce them to censor more content from their platforms. On March 25, the House Energy and Commerce Committee will interrogate Twitter’s Jack Dorsey, Facebooks’s Mark Zuckerberg and Google’s Sundar Pichai at a hearing which…