That makes Mr. Hannity the ultimate product of the Fox News Channel that Roger Ailes envisioned when he founded it with Rupert Murdoch 20 years ago, as a defiant answer to what they described as an overwhelmingly liberal mainstream news media that was biased against Republicans. Mr. Hannity was there from the beginning with Mr. Ailes, who was forced out over sexual harassment allegations last month.

Mr. Hannity’s show has all the trappings of traditional television news — the anchor desk, the graphics and the patina of authority that comes with being part of a news organization that also employs serious-minded journalists like Chris Wallace, Bret Baier and Megyn Kelly.

But because Mr. Hannity is “not a journalist,” he apparently feels free to work in the full service of his candidate without having to abide by journalism’s general requirements for substantiation and prohibitions against, say, regularly sharing advice with political campaigns.

So there was Mr. Hannity last week, devoting one of his shows to a town hall-style meeting with Mr. Trump at which his (leading) questions often contained extensive Trumpian talking points — including the debunked claim that Mr. Trump opposed the Iraq invasion. (As BuzzFeed News first reported, Mr. Trump voiced support for the campaign in a 2002 discussion with the radio host Howard Stern.)

On other days, he has lent his prime-time platform to wild, unsubstantiated accusations that Hillary Clinton is hiding severe health problems. He showed a video of a supposed possible seizure that was in fact a comical gesture Mrs. Clinton was making to reporters, as one of them, The Associated Press’s Lisa Lerer, reported. He also shared a report from the conservative site The Gateway Pundit that a member of Mrs. Clinton’s security detail appeared to be carrying a diazepam syringe, “for patients who experience recurrent seizures.”

A simple call to the Secret Service spokeswoman Nicole Mainor, as I made on Friday, would have resulted in the answer that the “syringe” was actually a small flashlight.

People in Mr. Hannity’s audience of 2.5 million who are inclined to believe the health allegations, and who believe the mainstream media are covering for Mrs. Clinton, are unlikely to be impressed by the Secret Service’s explanation.