The Hillary Clinton campaign and its allies, rallying behind the contention that cyberwarfare played a role in swinging the presidential election for Donald Trump, are now taking parting shots at the Obama administration, the intelligence community and the media for failing to treat the Russian hacking threat with sufficient urgency. Many Clinton confidants place blame for the Electoral College defeat squarely at the feet of FBI Director James B. Comey, arguing that his letter to Congress 11 days before the election reopening the investigation into Mrs. Clinton’s private email server turned the tide decisively in favor of Mr. Trump. But...