Washington (CNN) President Donald Trump started 2018 in a fury partly fueled by anger at his legal team for offering shifting timelines about when the Russia investigation would end, according to two sources familiar with the President's mindset.

The anger continued until midday Wednesday as Trump helped draft his blistering break-up letter to former chief strategist Steve Bannon, who offered a scathing attack on Trump and his family's handling of the Russia investigation.

That followed his taunting tweet Tuesday evening directed at North Korean leader Kim Jong Un , which caught many top administration officials off guard and prompted renewed worry among staff and allies about whether the President fully comprehends the risks he's taking in provoking adversaries. After Trump's North Korea broadside, aides inside the White House reached out to some of Trump's allies seen as having influence over the President to talk to him about his tweets and the risks they carry.

It's a bitter shift for a President who, just days ago, merrily rang in the New Year at his Florida resort dancing alongside a party-hatted first lady to Gloria Gaynor's persistence anthem "I Will Survive" and told The New York Times he felt special counsel Robert Mueller would treat him "fairly." Trump, who always loves his time at Mar a Lago, is readjusting to life in an icy Washington where the Russia probe looms and global flashpoints test his leadership skills with sometimes harrowing results.

This account of Trump's explosive first days of 2018 is based on interviews Wednesday with a dozen White House officials, lawmakers and other Republicans. It depicts a volatile President intent as ever on shaking the country's political norms, even as he faces crucial deadlines in the coming weeks on immigration and government funding.

Trump's venting began Tuesday with a 16-tweet onslaught that White House officials largely saw as an attempt by a media-obsessed President to whip up new storylines that center on him. But the fury escalated Wednesday as the first excerpts emerged from a bombshell portrait of Trump's first year in office.

Chafing at the Russia probe

Returning to the White House after more than a week at his Palm Beach estate, Trump has continued to chafe at the continuing Russia probe, which his legal team once told him would be over by the end of 2017. Trump's lawyers held talks with members of Mueller's team a few days before Christmas, a source briefed on the matter told CNN, and are no longer putting specific dates on when they expect the investigation to end.

Trump's White House lawyer did not respond to a request for comment on this story.

As CNN reported in December , some in Trump's inner circle prepared for him to explode in early 2018 if his lawyers' optimistic timeline about the Russia investigation wrapping up didn't come to fruition.

Trump's agitation at the Russia matter was only stoked Wednesday by Bannon's assertion, contained in author Michael Wolff's book "Fire and Fury: Inside the Trump White House," that a 2016 meeting between Trump associates and Russians was "treasonous."

People close to the President say the damning account of his first months in office contained within the book did not necessarily come as a surprise, though acknowledge the specific accusations lobbed by Bannon provided fresh reason to distance themselves from the onetime presidential aide.

White House press secretary Sarah Sanders, speaking at Wednesday's briefing, described Trump as "disgusted" by Bannon's remarks.

"Steve Bannon has nothing to do with me or my presidency. When he was fired, he not only lost his job, he lost his mind," Trump wrote in a blistering statement, which he crafted with the help of aides.

As is often the case, Trump's mood this week has gone through rapid upheavals. On Wednesday morning, Trump was described as furious at the allegations contained the excerpts from Wolff's book. Later, visitors to the West Wing described Trump as cheerful, even amid the tumult left in the wake of his tweets and the public falling-out with Bannon. The aides with whom Bannon sparred, including senior adviser Jared Kushner, carried with them an air of vindication that their disdain for the Breitbart chairman appeared well-founded, the people said.

Crossing a line

A source close to the White House said Bannon crossed a clear line by going after the President's family. "Once Bannon got personal, the gloves were off. They are holding nothing back," this source said.

The Bannon dust-up came as the White House was still grappling with Trump's declaration the night before that his "nuclear button" was larger than North Korea's Kim Jong Un's, a childish taunt that sent tremors of distress through national security circles.

Most White House aides concede there's been little formal attempt at this stage to rein in Trump's tweets, despite past consideration of imposing a system of vetting on the more controversial ones. Trump largely controls his Twitter account himself with the help of Dan Scavino, the director of social media, who enjoys top-ranking "assistant to the President" status.

During Trump's working days in the Oval Office, his tweets stick largely to script, including messages yesterday about the work his Veterans Affairs secretary and congratulating retiring Sen. Orrin Hatch on his long career.

Trump arrived back in the Oval Office just past 11 a.m. Tuesday and spent the day moving back and forth between the West Wing and his private residence, according to aides, who said he returned to Washington after a largely news-free vacation eager to reinsert himself in the days headlines and newscasts.

As is his custom, Trump returned to his third-floor residence just after 5 p.m. and clicked his large flat-panel television onto Fox News. Midway through the 7 p.m. hour, discussion turned to Kim's comment about his "nuclear button," which the North Korean leader boasted on Sunday was at his immediate disposal.

Twelve minutes later, the President had a response.

"North Korean Leader Kim Jong Un just stated that the 'Nuclear Button is on his desk at all times,'" Trump wrote. "Will someone from his depleted and food starved regime please inform him that I too have a Nuclear Button, but it is a much bigger & more powerful one than his, and my Button works!"

Blindsided advisers

The only button on Trump's Oval Office desk summons a valet who most often comes bearing a Diet Coke. Still, the taunt prompted immediate concern. Trump's top national security advisers were blindsided. Secretary of State Rex Tillerson was returning to Washington from Texas on Tuesday evening. And Kirstjen Nielsen, the newly installed Homeland Security secretary, appeared unaware of the bombastic rhetoric while speaking with reporters in California.

"I have not seen the tweet as I've been working with you all this afternoon," she said after surveying damage from last month's wildfires. "The President speaks for himself — I think we have to continue as he said to take the threat from North Korea very seriously."

On Wednesday, the White House and the State Department insisted the administration's policy toward North Korea has not changed — a statement that obscured the worry among some officials that Trump's tweet could provoke nuclear war.

"I think it shows really poor judgment for the President to perform the way he does. Particularly with tweets," former Vice President Joe Biden told CNN on Capitol Hill on Wednesday. "I think the President has to come to better understand that words matter coming from a president. There's a reason why it's important to be presidential. It's not just style. There's consequences. Severe consequences."

One White House official insisted on Wednesday morning there were no heightened anxieties in the West Wing after Trump's nuclear tweet, even amid hand-wringing by national security experts inside and outside the administration.

"I wouldn't psychoanalyze it," one official said of the President's Twitter feed, despite the tremors it prompts in foreign capitals and in the hallways of the State Department and Pentagon. Another official shrugged off the tweet as another of Trump's attempts to speak unfiltered to his supporters.

On Sunday evening, Trump appeared unaware of Kim's button comments when asked about them on a red carpet leading into his glamorous New Year's Eve gala at Mar-a-Lago.

"We'll see, we'll see," the tuxedo-clad President said, without elaborating. Standing alongside his wife Melania, festooned in sequins, and his 11-year-old son Barron, Trump instead invited reporters to join him at the party.

People who spoke with Trump over his 10-day stay in Florida described him as upbeat and relaxed-seeming. Inside the cosseted Mar-a-Lago grounds, Trump was surrounded by family — including sons Donald Jr. and Eric, and daughter Ivanka and her husband Kushner — as well as the longtime friends he's relied on for advice over the first year of his presidency.

Inside his club and on his golf course, Trump told his confidants that he has relished his first year in office.

"He said he loves it," said Fred Funk, the professional golfer who played with Trump on Monday. "He said he loves the aspect of being the President, and all the pressures that go along with it."

But privately, some of Trump's associates said they sensed a change in Trump. While he seemed at times the same garrulous host from earlier years, at other moments he was more withdrawn and less eager to engage with the members of his club, some of whom chafed at the less-accessible owner.

Speaking at his New Year's Eve dinner, Trump made little attempt to bury last year's grievances. Instead, he previewed the combative days ahead.

"We have some pretty good enemies out there, but step by step they're being defeated," he told the black tie crowd. "They're some bad people. Bad people. But that's ok. Someday maybe they'll love us."