Donald Trump's mental health has become the subject of media speculation. (AP Photo/David Zalubowski)

On MSNBC on Wednesday morning, Joe Scarborough floated the idea that Donald Trump might be a sociopath.

"We’re asking ourselves — I didn’t say this, but this is what everybody is saying: Is Donald Trump a sociopath?" the "Morning Joe" co-host said to guest Ari Fleischer, former press secretary for President George W. Bush. "Am I voting for a sociopath? And I know you’ve heard it because I’ve heard it. And all my Republican friends have heard it."

The unusual thing about Scarborough's comment is that it wasn't all that unusual. It is becoming commonplace for people in the media to wonder about the mental health of a major-party nominee for president of the United States.

This is not a normal, every-four-years kind of trend.

To be clear, we're not talking about the sort of casual, "he's crazy" remarks people throw around in everyday conversations; we're talking about actual, clinical mental illness.

Some of the speculation is based on observations from legitimate medical professionals. For example, Jeffrey Flier, the former dean of Harvard Medical School who remains a professor there, tweeted over the weekend that Trump "defines" narcissistic personality disorder.

In June, the Atlantic published a 9,000-word story about Trump's mental health by Dan P. McAdams, a professor of psychology and the director of the Foley Center for the Study of Lives at Northwestern University.

"Across his lifetime, Donald Trump has exhibited a trait profile that you would not expect of a U.S. president: sky-high extroversion combined with off-the-chart low agreeableness," McAdams wrote.

Professionals are often reluctant to make diagnoses from afar (Flier acknowledged he could be wrong about Trump's narcissism), and they generally discourage the rest of us from doing the same. But that hasn't stopped media types from playing amateur psychologist.

"Together, let's elect a sane, competent person," billionaire media mogul Michael Bloomberg said at the Democratic National Convention last week. His description of Hillary Clinton as "sane" seemed to suggest that Trump is not.

Here is former New York City mayor Michael Bloomberg's full speech at the Democratic convention. (The Washington Post)

Huffington Post editor in chief Arianna Huffington said in April that "Donald Trump displays all the symptoms of what the American Academy of Sleep Medicine has described as symptoms of chronic sleep deprivation."

HuffPo writers have multiple theories about Trump's brain. On Monday, Lev Raphael wondered: "Could there also be something medically, neurologically wrong with him? That’s a serious question." A day earlier, Daniel Wagner wrote that "Mr. Trump appears to be suffering from Narcissistic Personality Disorder (NPD)." Richard North Patterson offered the same diagnosis in June.

Here at The Fix, we've also tackled the question of whether Trump meets the definition of a narcissist, and elsewhere at The Washington Post, Plum Line blogger Greg Sargent wrote Tuesday about Trump's "ongoing, ever-worsening, seemingly sociopathic display of abusive tendencies."

On Tuesday, MSNBC's Lawrence O'Donnell told viewers "it's becoming more and more clear that the biggest disqualifying factor of Donald Trump as president is his mental health."

Over the weekend, HBO's John Oliver combined diagnoses when he labeled Trump a "sociopathic narcissist."

And the New Yorker recently published a story about Trump's co-author on "The Art of the Deal," who said if he were to write the same book today, he would call it "The Sociopath."

Slate's Elliot Hannon — perhaps poking fun at the extent of the media's psychological analyses — wrote Monday about that photo of Trump eating KFC. Headline "Donald Trump eats fried chicken like a sociopath (with a knife and fork)." This is where we are in 2016.

Some on the right side of the media have their own theories about the allegedly compromised state of Hillary Clinton's mental health. The Drudge Report on Wednesday promoted a Townhall story about a Benghazi victim's father who believes the Democratic presidential nominee might have a faulty memory of the attack because of a head injury.

Clinton fainted and suffered a concussion in December 2012. The idea that lingering concussion symptoms could compromise Clinton's ability to serve as president also has been featured in such publications as the National Enquirer and World Net Daily.

While questions about Clinton's mental health remain mostly on the fringe, however, doubts about Trump's psychological suitability are working their way into the mainstream.