Wednesday promises to be another stressful day for Facebook, Google and Twitter. Their chief executives will be grilled by senators about whether social media companies abuse their power. For Republicans, this is the opportunity they’ve been waiting for. Two weeks ago, Twitter prevented people posting links to a critical New York Post investigation into Joe Biden. It then apologised for failing to explain its reasoning before ditching a rule it had used to justify the action. For many Republicans, this was the final straw – incontrovertible evidence that social media is biased against conservatives. The accusation is that Silicon Valley is at its core liberal and a bad arbiter of what’s acceptable on its platforms.