In a phone interview with CNN on Saturday, J. Brien Comey called his son's firing last week "a Trump deal."
"[Comey] didn't give him 100% loyalty, and he demands that of people who work with him," the 86-year-old said. "[Comey] said he would give 100% honesty, but not loyalty."
Comey said his son, whom he described as a "straightforward and honest guy," was fired "because Jim tells the truth, (while) Trump runs around lying most of the day."
The remarks come after a tumultuous couple of weeks for the Trump administration, which saw Trump fire the FBI director May 9 and then undermine his own senior aides
on his reasons for doing so -- moves then capped by a report
in The New York Times that Trump discussed the dismissal in meeting with senior Russian officials in the Oval Office the day after Comey's ouster.
"I just fired the head of the FBI," Trump told the Russians, according to a document summarizing the meeting that was read to the Times. "He was crazy, a real nut job. I faced great pressure because of Russia. That's taken off."
The White House did not respond immediately to a request for comment on J. Brien Comey's statements.
Unlike the former FBI director, who so far has kept quiet about his firing, Comey's father had some very strong words about the FBI director's dismissal.
"Why he was fired, I think, is Trump changes every day," he said. "He had three reasons three days in a row."
The elder Comey did not hide his own distaste for the President saying,"Oh my God, I think he should be impeached immediately -- yesterday. He's a very incompetent guy. He's out of his league."
But he conceded that he thought impeachment "a long shot."
"(Comey) could have been subservient to Trump, (but I told him) he was not going to do that ..." J. Brien Comey said, adding tongue-in-cheek: "Incidentally, I told him I thought he and Trump would testify side by side in front of these congressional committees. He just kind of laughed."
Comey's father said he has never been a fan of Trump and didn't vote for him: "I think the man should be in a home quite honestly, he's crazy as a hoot."
But he didn't vote for Hillary Clinton either. "I am not going to tell you what I think of her," he said. "We had lousy choices."
The elder Comey, who first spoke to New Jersey's The Record
about his son's firing, said he preferred Republican Ohio Governor John Kasich during the 2016 Republican presidential primary because he "seemed like a very honest guy. He made a good impression on me. I thought he would make a good president."
Comey said he has a close relationship with his son, whom he sees on holidays, and had just spoken with him earlier Saturday morning. He is expecting a visit from Comey and his wife to his New Jersey home in a few weeks -- the same house where Comey grew up with his three siblings.
Comey is coping well with his termination and the storm that originated from it, his dad said.
"He's doing fine. He's a solid citizen, he has lots of opportunity," he said. "It was a dumb thing to get rid of him. A loss for the FBI."
When asked what his son thinks will now happen to the FBI's investigation of contacts between Trump campaign aides and Russians, Comey said he didn't know.
"We never talked about that stuff," he said.