WASHINGTON — In the days after President Trump fired James B. Comey as F.B.I. director, law enforcement officials became so concerned by the president’s behavior that they began investigating whether he had been working on behalf of Russia against American interests, according to former law enforcement officials and others familiar with the investigation.
The inquiry carried explosive implications. Counterintelligence investigators had to consider whether the president’s own actions constituted a possible threat to national security. Agents also sought to determine whether Mr. Trump was knowingly working for Russia or had unwittingly fallen under Moscow’s influence.
The investigation the F.B.I. opened into Mr. Trump also had a criminal aspect, which has long been publicly known: whether his firing of Mr. Comey constituted obstruction of justice.
So what happened to the investigation:
The special counsel, Robert S. Mueller III, took over the inquiry into Mr. Trump when he was appointed, days after F.B.I. officials opened it. That inquiry is part of Mr. Mueller’s broader examination of how Russian operatives interfered in the 2016 election and whether any Trump associates conspired with them. It is unclear whether Mr. Mueller is still pursuing the counterintelligence matter, and some former law enforcement officials outside the investigation have questioned whether agents overstepped in opening it.