The F.B.I. and Justice Department faced a hard decision in two investigations this past summer that had the potential to rock the presidential election. The first case involved Donald J. Trump’s campaign chairman, Paul Manafort, and secretive business dealings in Ukraine. The second focused on Hillary Clinton’s relationships with donors to her family foundation.

At the urging of the Justice Department, the F.B.I. agreed not to issue subpoenas or take other steps that would make the cases public so close to the election, according to federal law enforcement officials…

Former senior law enforcement officials in both parties, though, say Mr. Comey’s decision to break with Justice Department guidelines caused these problems. Had he handled the case the way the F.B.I. handled its investigations into the Clinton Foundation and Mr. Manafort over the summer, the argument goes, he would have endured criticism from Republicans in the future but would have preserved a larger principle that has guided cases involving both parties.