Mark Warner: the tech-savvy senator taking Silicon Valley to task

As executives from Facebook, Google and Twitter prepare to testify on Capitol Hill, one Democrat has emerged as a formidable critic

Last month, Senator Mark Warner left a closed-door briefing with Twitter visibly frustrated. He said he doubted whether the tech titan grasped the gravity of the investigation into Russian election meddling, and fumed to reporters that the company's presentation to congressional investigators about how Russia used its platform to influence the 2016 race was "frankly, inadequate on every level".

The public scolding was yet another sign of Washington's growing impatience at Silicon Valley, with the Virginia senator emerging as one of the loudest critics in Congress. This month he co-authored new legislation that would require internet companies to disclose who purchased online political ads on their platforms, the most aggressive attempt yet to regulate big tech.