Trump claimed the investigation into his 2016 rival's private email server was "obviously a fix." He called Comey "the best thing that ever happened" to Clinton.
Trump apparently responded to a Newsweek report, citing FBI records, that says Comey drafted a statement about the Clinton email investigation's conclusions two months before he issued it. In July 2016, Comey called Clinton "careless" in her use of a private server while at the State Department but recommended that the Justice Department not charge her with a crime.
Congressional Republicans like Senate Judiciary Committee Chairman Sen. Chuck Grassley on Iowa have raised questions to the FBI about Comey's conduct in the investigation. It is not clear if drafting the statement violates the department's protocols.
The FBI declined to comment.
Trump's fixation on Comey comes as special counsel Robert Mueller continues his investigation into Russian efforts to influence the election and possible collusion with the Trump campaign. Trump's decision to fire Comey in May in the thick of the probe is reportedly part of the investigation.
The White House initially said Trump fired Comey because the Justice Department criticized the former FBI director's handling of the Clinton probe. But Trump later admitted he would have terminated Comey regardless of what the Justice Department said.
In Wednesday's tweets, Trump signaled that he wants his attorney general to look into Comey, asking "Where is Justice Dept?"
Trump again accused Comey of leaking classified information. The president did not say what information specifically, though he has previously accused the ex-FBI director of leaking sensitive information when Comey told a friend to share the contents of a memo he wrote with The New York Times.
Comey has said he wrote the memo that he shared in a way that would make it unclassified.
Clinton, for her part, partly blames her election loss on Comey. In late October, just days before the election, Comey said he found new emails relevant to the Clinton probe. It shifted the focus back to the investigation for much of the election's final stretch.
Comey announced two days before the election that the new emails did not change the FBI's findings.