Could it be the left's next line of relentless attack against President Donald Trump?

Now members of the left, mainstream media, pollsters, psychological professionals and even some Republicans are declaring Trump mentally unfit for the office of the presidency.

Trump's detractors have long suggested he is unstable, even a narcissist and a man exhibiting erratic behavior. While the topic has come up sporadically over the last couple of years, Democrats now appear to be plotting a serious and coordinated attack on Trump's mental fitness for office.

After President Trump's speech in Phoenix, Arizona, Tuesday evening, even James Clapper, who held top intelligence positions during the administrations of Presidents George W. Bush and Barack Obama, called into question Trump's "fitness to be in office."

TRENDING: Trump identifies Judges Amy Coney Barrett, Barbara Lagoa as possible SCOTUS front-runners: Report

"I really question his ability to be – his fitness to be – in this office," Clapper said.

He also told CNN: "If in a fit of pique he decides to do something about Kim Jong-un, there's actually very little to stop him. The whole system is built to ensure rapid response if necessary. So there's very little in the way of controls over exercising a nuclear option, which is pretty damn scary."

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Others, both Democrat and Republican, have piled on:

Not just 'crazy talk': Left pursues action in Congress

It's not all just talk. Democrats are increasingly supporting legislation suggesting Trump is mentally incompetent to perform his duties. In April, Rep. Jamie Raskin, D-Md., sponsored the "Oversight Commission on Presidential Capacity Act," which would establish a commission to determine if a president no longer has physical or mental capacity to perform the duties of his office.

As of this report, 28 Democrats have signed on as co-sponsors. Raskin told USA Today he's seen "a sudden spike [in co-sponsors] after every acute episode" of seemingly erratic behavior by Trump. More co-sponsors may be added after Congress comes back into session on Sept. 5.

Meanwhile, California Democrats are reportedly leading the attacks over Trump's mental health.

Rep. Ted Lieu, D-Calif., unveiled a bill in February requiring the presence of a psychiatrist in the White House.

Last week, Rep. Zoe Lofgren, D-Calif., introduced a resolution in Congress that called on Trump to seek a medical and psychiatric evaluation that would determine whether he's fit for office. She questioned if Trump has "early stage dementia" and whether "the stress of office aggravated a mental illness crippling impulse control."

Rep. Jackie Speier, D-Calif., called on Vice President Mike Pence and the Trump cabinet to invoke the 25th Amendment, which empowers them to remove a president who is deemed incapable of serving in the position.

"[Trump] has demonstrated that his mental capacity and his erratic behavior are issues we need to be concerned about for our national security," Speier told Politico. "And I think I'm not the first person that's talked about it. I'm just the first person that's been public about it."

Yale forensic psychiatrist Bandy Lee, editor of the book "The Dangerous Case of Donald Trump," is working with other psychiatrists and Democrats in Congress to form a panel that would advise Congress on Trump's mental status. Lee claims she is speaking out because of Trump's "dangerousness," according to USA Today.

Another psychiatrist, Allen Frances, who came up with the official definition of narcissistic personality disorder, is set to debut his own book next month, "Twilight of American Sanity: A Psychiatrist Analyzes the Age of Trump."

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As WND reported, without ever having examined Trump, psychological professionals already have called the president "psychotic," "narcissistic," "paranoid," "hypomanic," "emotionally unstable," "delusional" and "psychologically isolated" and claimed he has a "dangerous mental illness." One physician suggested Trump could be suffering from an untreated sexually transmitted disease known as neurosyphilis.

And in July, a national psychology organization gave psychoanalysts the green light to publicly comment on Trump's mental health. The executive committee of the American Psychoanalytic Association, or APsaA, announced in an email that it will allow its 3,500 members to speak more openly about the president's mental health. The email noted that its "ethical code concerns clinical practice, not public commentary."

The purpose for the group's email announcement was "belief in the value of psychoanalytic knowledge in explaining human behavior," APsaA past president Dr. Prudence Gourguechon, a Chicago psychiatrist, told health news website Stat News. "We don't want to prohibit our members from using their knowledge responsibly."

Gourguechon told the publication mental health practitioners have a great responsibility to share their insight "since Trump's behavior is so different from anything we've seen before" in a U.S. president.

Even the pollsters are getting in on the action, revealing findings that appear to show Americans are growing concerned.

A Morning Consult poll conducted Aug. 17-19 among 1,987 registered voters claimed 55 percent of respondents said Trump is not stable.

And a new George Washington University Battleground Poll found that 71 percent of voters polled said Trump's "behavior is not what I expected from a president."

Double standard? Media, Dems were silent on Hillary's mental, physical health

By contrast, the same Democrats and media organizations curiously expressed little concern for Democratic Party nominee Hillary Clinton's physical and mental health, ignoring her alarming physical symptoms and apparent history of unhinged and even violent outbursts.

On multiple occasions during the 2016 presidential campaign, Hillary was being physically propped up during her speeches. Though Hillary's health has been largely ignored by the establishment media, there have been questions about her health, from her tripping and falling, to reports of blood clots, to special glasses that she used during the Benghazi congressional hearings and other concerns about her explosive temper.

In "Hillary Unhinged," find out who the true Hillary is with a raw and humorous collection of quotes that pitilessly underscores her hypocrisy and endless pandering. Discover the REAL Hillary in her own words!

A video in August 2016 appeared to show her in what the popular Drudge Report described as a “brain freeze.” And that followed earlier episodes that had some questioning whether she was suffering a seizures.

And on Sept. 11, 2016, Hillary prematurely left a memorial service marking the 15th anniversary of 9/11 in New York City, walking gingerly and collapsing as aides tried to get her into a van.

Watch a slow-motion video of Hillary Clinton appearing to faint:

While she was secretary of state, Hillary fainted and sustained a serious concussion and a blood clot on her brain. Former President Bill Clinton said it took "six months of very serious work" for her to recuperate.

After her 11-hour Benghazi testimony in 2015, Hillary nearly collapsed as she walked to her car. Aides rushed to physically support her and usher her into the back seat.

Also, Hillary apparently exhibited volatile behavior during the presidential campaign and in previous years. Her epic tantrums continuously plagued her 2016 presidential campaign, according to the book, "Shattered: Inside Hillary Clinton's Doomed Campaign," by political writers Jonathan Allen and Amie Parnes, who claim to have had "deep access to insiders from the top to the bottom of the campaign."

Despite all her curious behavior and troubling symptoms, the mainstream media and members of Congress expressed little to no concern for her physical and mental fitness for the office of president.

Aside from her physical symptoms, Hillary has a long history of bizarre and expletive-laced outbursts, even physical violence.

As WND reported, Hillary, who was Arkansas' "Mother of the Year" in 1984, was said to have grown frustrated that handicapped children weren't collecting their Easter eggs quickly enough on the lawn of the Arkansas governor's mansion. That's when she reportedly shouted, "When are they going to get those f---ing ree-tards out of here?!"

Dolly Kyle – a childhood sweetheart of Bill Clinton who had a 33-year relationship with him – said Hillary used the terms "stupid kike" and "f---ing Jew bastard" before "condemning all Southerners for racism."

Other Clinton acquaintances, reporters and staffers through the years have also claimed Hillary has an explosive temper and has frequently become unhinged.

Meet the REAL Hillary! Top 36 Hillary F-bombs, flip-outs and eye-popping tantrums

After learning of Bill's affair with White House intern Monica Lewinsky in 1998, Hillary is said to have handled the situation by bloodying her husband's head.

"There was blood all over the president and first lady's bed," wrote former White House reporter Kate Anderson Brower in yet another book, "The Residence: Inside the Private World of the White House." "A member of the residence staff got a frantic call from the maid who found the mess. Someone needed to come quickly and inspect the damage. The blood was Clinton's. The president had to get several stitches in his head."

Another staffer, White House florist Ronn Payne, also recalled a heated argument between Bill and Hillary.

“He was coming up the service elevator … as the Clintons argued viciously with each other. … [H]e heard the first lady bellow ‘goddamn bastard!’ at the president – and then he heard someone throw a heavy object across the room,” Brower wrote. “The rumor among the staff was that she threw a lamp. The butlers, Payne said, were told to clean up the mess. In an interview with Barbara Walters, Mrs. Clinton made light of the story … ‘I have a pretty good arm … If I’d thrown a lamp at somebody, I think you would have known about it.'”

Payne also recalled, “You heard so much foul language” in the Clinton White House.

Another alleged mistress of Bill's, Sally Miller, claimed Bill told her Hillary has snorted cocaine, but he tolerated it because "without it, Hillary's a raving maniac."

"My God, we've had to borrow money to replace lamps, chairs, all kinds of valuable s--t in the governor's mansion because of Hillary's temper," Miller said Bill once told her. "I've had to take Chelsea outside many times to keep her out of Hillary's 'line of fire.'"

In "Hillary Unhinged," find out who the true Hillary is with a raw and humorous collection of quotes that pitilessly underscores her hypocrisy and endless pandering. Discover the REAL Hillary in her own words!

In one June 2016 report, it was revealed Hillary hurled a Bible at a Secret Service agent's head, according to former agent Gary Byrne, who said her explosions grew worse as the Clintons' time in the White House went on.

Byrne warned Hillary was too "erratic, uncontrollable and occasionally violent" for the presidency.

Hillary has even "beaten Bill, hit him with hard objects, scratched and clawed him, and made him bleed," according to the 2015 book, "The Clintons' War on Women," by authors Robert Morrow and Roger Stone.

In October, WND published a list of the top 36 Hillary F-bombs, flip-outs and eye-popping tantrums.