WASHINGTON -- For U.S. President Donald Trump, this is a best-of-times, worst-of-times moment. So far.

The president was up early Saturday celebrating the Senate's overnight passage of a sweeping tax overhaul package that puts him on the cusp of a major legislative achievement that has so far eluded him. But within hours, he was tweeting and commenting about Russia, even in the midst of a victory tour in New York celebrating the advance of the tax overhaul.

That victory was clouded by Friday's news that Trump's former national security adviser, Michael Flynn, was pleading guilty to lying to the FBI about his Russian contacts during the presidential transition. Flynn is co-operating with special counsel Robert Mueller's Russia investigation, a potentially ominous sign for Trump.

The head-snapping developments in less than 24 hours underscored a reality of his presidency: He just can't escape Russia.

"I think the timing probably displeased him," said former Trump campaign aide Barry Bennett, an understatement about a man given to overstatement.

Indeed, while he was in a motorcade in New York City, going from one political fundraiser to the next. "There was nothing to hide!" said his tweet. He declared that he "had to fire General Flynn because he lied to the Vice-President and the FBI."

Trump called it "a shame" because Flynn's actions during the transition following the 2016 election "were lawful." He told reporters earlier there was no collusion between his campaign and Russia.

Flynn became the first member of the Trump White House to admit guilt in Mueller's criminal investigation. His co-operation with investigators could help build a case involving possible co-ordination between the Trump campaign and Russia to influence the 2016 U.S. presidential election.

While Trump has long dismissed the probe into whether his team colluded with Russia as "fake news," Flynn's move was a sobering reminder that the investigation is not going away.

And Trump's anger and frustration with the investigation have only served to compound the problem and further distract from his agenda. The president has insisted that the investigation is aimed at discrediting his unlikely triumph over Democratic rival Hillary Clinton and has made him look weak before world leaders. He's been anything but subtle in trying to make it go away.

In February, he told FBI Director James Comey he hoped the FBI would "let go" of an investigation into Flynn -- a comment Comey took as a presidential directive. Three months later, Trump fired him. Comey saw that as an effort to interfere with his investigation of Russia's ties to the Trump campaign.

The president hasn't been able to stop talking about the Russia probe. Over the summer he tweeted: "You are witnessing the single greatest WITCH HUNT in American political history - led by some very bad and conflicted people!"

This time, the initial White House response came from attorney Ty Cobb, who argued that "nothing" about the plea implicated anyone in the White House. Cobb pointedly referred to Flynn as a "former Obama administration official" who had worked for the Trump administration for just 25 days.

In October, Trump similarly sought to disassociate himself from his former campaign chairman Paul Manafort, who pleaded not guilty to felony charges of conspiracy against the United States and other counts, along with his business partner. Trump also dismissed George Papadopoulos, who admitted to lying to the FBI about his contacts with Russian intermediaries last year, as a "young, low level volunteer."

But that approach became more difficult with Flynn, who was a steady presence during Trump's campaign and was hired to become the president's top national security aide. "It's huge. It's rolling out like Watergate did," said GOP analyst Rick Tyler. "Now you have someone on the inside who is turning on the president and they've already distanced themselves."

Even as Mueller's team was disclosing the agreement with Flynn on Friday, Trump's team was notching progress on his plan to cut taxes and give the president a much-needed victory after multiple failed tries to overturn President Barack Obama's health care law.

Shortly after Flynn was charged, Senate Republican leaders signalled they had enough votes to pass the tax bill, the culmination of an intense lobbying campaign by the president and his allies.

With Pence presiding, the bill cleared the Senate early Saturday morning on a vote of 51-49, winning passage with the support of Senate Republicans who crossed Trump on his ill-fated health care legislation, such as Sens. John McCain of Arizona, Lisa Murkowski of Alaska and Susan Collins of Maine.

"On health care, in all candour, they struggled to lead," said Tim Phillips, president of Americans for Prosperity, the conservative group backed by the activist brothers David and Charles Koch. But he said Trump was on the verge of a "significant achievement" in guiding the tax overhaul through both chambers.

Trump aides who spent Thursday night at a White House holiday party spent Friday trying to process the jarring Flynn developments and pointing to the momentum on the tax bill as a positive development.

For a president who has already begun raising money and preparing for his re-election campaign, Trump's advisers and allies argued the tax bill would be far more consequential to his 2020 campaign than the Mueller probe.

Yet the magnitude of the sweeping investigation was reflected in the stock market, the barometer that Trump frequently points to as an affirmation of his economic stewardship. Shortly after news of Flynn's guilty plea spread, the Dow Jones industrial average sank more than 300 points before recovering most of that ground during the afternoon.

Shortly after the tax bill passed the Senate, Trump tweeted: "We are one step closer to delivering MASSIVE tax cuts for working families across America."

He seemed to be betting that Americans will care more about tax cuts than the investigation moving deeper into his White House.

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Ken Thomas and Catherine Lucey cover the White House and national politics for The Associated Press.