President Trump lashed out Saturday on Twitter in response to charges that he is unfit for office, writing that “mental stability and being, like, really smart” have long been his two greatest assets. (Jabin Botsford/The Washington Post)

In a White House marked by a string of high-level comings and goings, an extraordinary level of palace intrigue and a general sense of unpredictability, there remains but one constant. That is the disorder at the center, perpetrated by a president who continues to break the norms of his office. It's the reason 2018 could eclipse 2017 for political turbulence.

The first week of the year was breathtaking for its shock value: a presidential tweetstorm of personal animus and policy provocation that overshadowed positive news about the economy. That has become the running story of the Trump presidency: a chief executive whose personal behavior has become the administration's defining feature rather than the gains of a growing economy or the significant course reversal from the Obama years.

The tweets took another stunning turn on Saturday morning, when the president defended himself against charges that he lacks the fitness for office. He accused "Democrats and their lapdogs" and the "Fake News Mainstream Media" of going after him the way he said they went after President Ronald Reagan, by "screaming mental stability and intelligence."

Trump said that "mental stability and being, like, really smart" have long been his two greatest assets. Winning the presidency on his first try, he insisted, should be seen as "genius…and a very stable genius at that!"

The tweets were in response to renewed discussion about the president's mental fitness prompted by the portrait of Trump in Michael Wolff's scathing new book, "Fire and Fury."

White House press secretary Sarah Huckabee Sanders denounced the book as "trashy tabloid fiction." The book has obvious flaws and errors — in one case, Wolff puts a Washington Post reporter, Mark Berman, at a power breakfast scene at the Four Seasons Hotel in Georgetown, a place Berman says he has never been — and Wolff has drawn past criticism for not adhering to rigorous journalistic standards in his works. It appears it was lobbyist Mike Berman who attended the breakfast, Post reporter Berman pointed out on social media.

So there are errors in the book, and that must be considered in any evaluation of its merits. Yet Wolff's portrait of chaos and dysfunction inside the White House is consistent with the reporting by White House correspondents at The Post, the New York Times, Politico, cable networks and others, almost from Day One of the Trump presidency.

Is that portrait exaggerated? Some insiders insist it is, that in the White House, particularly under current Chief of Staff John F. Kelly and after the departure of Stephen K. Bannon and the lowering of Jared Kushner's profile, day-to-day operations are less chaotic than they were during the first half of 2017. Routine activity gets done. Major policy activity is taking place. Judicial nominations are being pushed to Capitol Hill. A major tax bill has been signed into law.

That, however, ignores the elephant in the room, which is how the president operates and the degree to which he manages to overshadow everything else. On that front, Wolff's book offers a worrisome portrait of an incurious president with a short attention span, a volatile chief executive who rails against his critics and who at moments appears isolated by his frustrations.

More concerning is the suggestion that this is a president whose behavior alarms those who work with him most closely. That too has been reported before. There are some fresh anecdotes in the book, but this is hardly the first time the president has been cast in a highly unflattering way.

Months ago, Sen. Bob Corker (R-Tenn.), who as chairman of the Foreign Relations Committee has spent time with Trump and senior national security officials, said, "The president has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful." He later described the White House as "adult day care."

Secretary of State Rex Tillerson was quoted by NBC News as calling the president "a moron" in a private meeting in July at the Pentagon. Despite several opportunities, Tillerson has never disavowed that comment. "I'm not dignifying the question with an answer," he told CNN's Jake Tapper in October after Tapper repeatedly pressed him to say whether he had used the words. Tillerson told CNN this past week that he has "never questioned" the president's "mental fitness."

There is a difference between the words attributed to the secretary of state and those by Corker, though they could easily move people to a similar conclusion. In Tillerson's case, the characterization is not about stability but rather knowledge — concerning if the country's chief diplomat does not think the president he serves understands the complexities of national security issues.

The same has been said in more delicate ways about the president's understanding of other issues. He came to the presidency with no background in government or policy. No one credited him with mastering the details of the health-care bills that Republicans were trying to enact in an effort to get rid of the Affordable Care Act. That was one reason he was an ineffective salesman in that fight.

Nor is it always necessary for a president to be expert in the details of all issues. President Jimmy Carter drew criticism for being too much a micromanager and for getting mired in the details of policy rather than focusing on bigger questions. Reagan was belittled as a president who paid little attention to policy details but lauded for his ability to know his convictions and to chart a clear course to accomplish his goals.

So the question of what the president knows, while important, is not the most significant question. Corker's comment about the president's stability, and the president's decision to highlight that issue with his tweets on Saturday, assures that a conversation that has been gathering force will intensify. Though to what end?

Trump has repeatedly behaved as has no other modern president, and that's based just on things the public has been able to see. Meanwhile, almost every news organization has reported about the private rages, the lack of focus, the indiscipline and the isolation that also define the style of the 45th president. Through the first week of 2018, he was barely seen in public until he left for Camp David on Friday, his bully pulpit reduced to his social media platform.

The frustration stems in no small part from the ongoing investigation led by special counsel Robert S. Mueller III. Where this all leads remains in Mueller's hands, but if the president thought the probe was near its conclusion, he was fooling himself. Perhaps that's what turned the beginning of the new year into one so unsettling.

The president wants the public to focus on things such as the rising stock market, which just saw the Dow break through 25,000 as if that barrier were mere tissue, and a jobs report that showed the unemployment rate in the last month of 2017 at a 17-year low. The new tax bill, he argues, will accelerate those trends. Perhaps.

But despite all that, Trump continues to make himself the issue. The past week proved it once again, and Saturday's tweets added a startling exclamation point.