Washington (CNN) President Donald Trump , who was already incensed by the idea that his accomplishments weren't getting the credit they deserve, grew more worried on Friday after news broke that Michael Flynn , his former national security adviser and longtime campaign aide, pleaded guilty for lying to the FBI.

"I think that Russia investigation is wearing on all of us, the President most of all," said a source close to Trump. "But I think he is more concerned about the state of his accomplishments and this presidency."

Flynn's plea is the closest that Special Counsel Robert Mueller's probe into the Trump campaign's possible connection to Russian meddling in the 2016 election has come to the Oval Office. It was a dramatic step for an investigation that has infuriated Trump since its creation. Flynn spent countless hours briefing the businessman-turned-politician during the 2016 campaign and was Trump's top national security aide.

How it unfolded

Trump was briefed on Flynn's plea deal on Friday morning, a senior White House official told CNN. The president, the source said, had anticipated Flynn would get swept up into Mueller's investigation for weeks.

Externally, Trump's top aides and surrogates were trying to spin the news as a positive step for Trump that signals Mueller's investigation could soon be wrapping up. A senior White House official said Friday that the president is feeling "no anxiety" about the situation.

Another source close to the White House described the President and his team as in denial on the Russia investigation. They are "totally in a bubble."

This source said the White House should be taking the Flynn news much more seriously. "This is like a red alert," the source said.

But the source said White House officials said the President expects to be cleared by Mueller's team before much longer.

"They think he's going to be exonerated very soon," the source added.

In more reflective moments, though, Trump confidants acknowledge that the President is bothered by the Flynn news, particularly because he is worried that another deluge of stories about Russia could overshadow his achievements.

"Every single one of us has come to expect this, including the President," a source close to Trump said of the Flynn news. "The worry is this could cool down what is otherwise a pretty strong march towards the economic growth we need."

The source acknowledged that Flynn's plea -- along with indictments of former Trump campaign aides Paul Manafort and Rick Gates and another plea by former Trump campaign foreign policy adviser George Papadopoulos in October -- "damage Trump's ability to get things done."

A manifestation of this frustration: As Trump's White House aides devised a communication strategy for Flynn's plea, Republicans in the Senate said they had the votes to pass the Trump-backed tax plan, an achievement the Trump White House has longed for.

Even as aides swore all was well within the White House, Trump was noticeably kept at arms-length for much of the day. When Prime Minister Fayez al-Sarraj of Libya stepped out of his car, the at-times loquacious Trump ignored shouted questions. And a previously planned photo-op with Trump and al-Sarraj was abruptly canceled as reporters waited outside the Oval Office.

Clearest sign yet

Mueller's court filings are the clearest sign yet of potential coordination between Flynn and a top Trump advisers regarding contact with Russian officials. CNN reported on Friday that Jared Kushner -- Trump' son-in-law and top adviser -- was the "very senior member of the Presidential Transition Team" who directed Flynn to contact the Russian ambassador and other countries on an upcoming UN Security Council vote on Israeli settlements.

The probe is now zeroing in on Trump's inner circle , making it harder for the Trump administration to distance itself from the action. When Manafort and Gates were indicted, multiple Trump sources told CNN the indictments had nothing to do with the White House because the duo never worked for Trump as president.

That isn't the case for Flynn, who was Trump's top national security aide for less than a month before he was fired for lying to the Vice President Mike Pence.

Trump, according to multiple sources, considered Flynn a friend, enjoyed his company on the campaign trail and in the White House and believed that the retired United States Army Lieutenant General was an honorable person.

JUST WATCHED Trump's praise of Michael Flynn over the years Replay More Videos ... MUST WATCH Trump's praise of Michael Flynn over the years 01:52

That means even though he canned his longtime aide under pressure in February, Friday's news was likely still difficult to take. Trump said earlier this year that Flynn was a "wonderful man" who has been "treated unfairly."

The President "feels sorry for Flynn," a senior White House official said, because he "likes" the former national security adviser. The official add that Trump is "thinking about Flynn and his family" during this time.

One source close to the Trump added that the White House was balancing the fact that "the President was close to Flynn and spent a great deal of time with him" and "the truisms that General Flynn created his own problems here."

As for a presidential pardon for Flynn, the senior White House official said that was "absolutely not under consideration."

While Trump was bothered by Flynn's guilty plea, aides close to Pence feel vindicated because the former national security adviser was fired for lying to Pence in the first place.

What Flynn admitted Friday is "what we have known all along," a source told CNN. Flynn, the source said, lied to the vice president and he lied on the same matter to federal authorities.