WASHINGTON — America’s intelligence chiefs sat down with members of Congress behind closed doors on Friday for what they thought would be a straightforward briefing on Russian cyberattacks. What ensued instead was a confrontation Democrats have long sought with James B. Comey, the director of the Federal Bureau of Investigation. Why, the House Democrats demanded to know, did Mr. Comey believe it was O.K. to make repeated disclosures during the campaign about the investigation into Hillary Clinton’s emails but to this day refuse to say if the F.B.I. is investigating links between the Trump campaign and Russia? His answers did...