But the investigation by Mr. Horowitz, who has maintained a reputation for being above the partisan fray, may have a better chance of being accepted across party lines as credible. Mr. Horowitz, who is expected to release a much-anticipated report of his findings in the coming weeks, is believed to be weighing whether to recommend that the Justice Department tighten rules for any future counterintelligence investigations of a presidential campaign, which was a novel dilemma in 2016, according to people familiar with aspects of his investigation.