If prosecutors want the building blocks for a claim that President Donald Trump interfered with a federal investigation, legal experts say fired FBI Director James Comey has handed those over. They say he did it by recounting details of interactions that could show the president intended to obstruct justice. Comey this week has recounted conversations with Trump in which the president said he hoped Comey would let go of the FBI’s investigation of a former national security adviser. That’s coupled with Comey’s statement Thursday to a Senate panel that he believes Trump fired him in May to alter the bureau’s investigation of Russia’s role in the 2016 election. But proving obstruction of justice is difficult even in ordinary circumstances. Moreover, political and other legal factors decidedly weigh in Trump’s favor.