WASHINGTON -- President Donald Trump claimed vindication after nearly two years of unrelenting investigation on Sunday, seeing "complete and total exoneration" in the Justice Department's account of special counsel Robert Mueller's findings and signalling he was eager to go on offence in the political fight ahead.

A buoyant Trump reacted to the release of Mueller chief findings with a mix of celebration, personal grievance and calls for political retribution. He cast the investigation as politically motivated, and bemoaned the probe's toll on the country -- and on him.

"It was just announced there was no collusion with Russia." Trump said in brief remarks to reporters. "It's a shame that our country had to go through this. To be honest it's a shame that your president has had to go through this."

Trump spoke shortly after the Justice Department released a letter saying special counsel Robert Mueller's investigation did not find evidence that Trump's campaign "conspired or co-ordinated" with Russia to influence the 2016 presidential election.

The four-page summary by Attorney General William Barr was less definitive on the question of whether Trump obstructed the probe. Mueller's report "does not exonerate" on that issue and instead "sets out evidence on both sides of the question, " Barr wrote. Barr, however, said he found insufficient evidence of a crime on the issue.

Trump and his aides did not let that distinction -- between Mueller's findings and Barr's determination -- prevent them from declaring victory. Trump, speaking to reporters before boarding Air Force One, was clear he was ready to fight back against Democrats who have said they intend to use Mueller's report as a road map for further investigation into Trump and his inner circle.

"This was an illegal takedown that failed," he said, repeating his unproven claims that the investigation was launched by people trying to undermine his presidency after being devastated by Democrat Hillary Clinton's loss.

Trump's victory lap came after he kept a low profile over the weekend at his private club in Palm Beach, Florida. White House spokesman Hogan Gidley said Trump was briefed on Barr's letter in his residence by staff and attorneys. Gidley said Trump reaction was brief. "This is very good," he said, according to Gidley.

The White House, like lawmakers on Capitol Hill, has yet to see the full account by the special counsel.

Trump was visibly triumphant by the time he arrived at the White House Sunday evening. He pumped his fists at a group of supporters and told reporters, "I just want to tell you, America is the greatest place on Earth. The greatest place on Earth."

Meanwhile the president's aides breathed a collective sigh of relief upon reading the description of Mueller's findings. Even if not ensnared in the probe, many have faced public criticism and professional risk as the investigation lingered.

Trump's victory lap came after he kept a low profile over the weekend, heeding the advice of his lawyers, who warned him against tweeting about the probe before details were released. Trump spent Sunday golfing with Sen. Lindsey Graham, R-S.C., former Rep. Trey Gowdy, R-S.C., and his acting chief of staff, Mick Mulvaney, also a former South Carolina congressman, according to a White House official, as aides sought to keep the president busy during the tumultuous weekend.

A larger pack of aides than normal -- including press secretary Sarah Sanders -- travelled with Trump to Mar-a-Lago to manage any fallout. Trump was briefed on what his supporters would say on television throughout the weekend; aides hoped the president might stay quiet if he felt his messages were getting out even if he wasn't delivering them himself.

Trump spent the weekend surrounded by aides, friends and family, including son Donald Trump Jr. and his girlfriend Kimberly Guilfoyle, who are at the Florida estate for spring break with their children. Trump's eldest son was out fishing with his children when the report was delivered.

The president and first lady Melania Trump celebrated their son Barron's 13th birthday with dinner on the patio of Mar-a-Lago on Friday night. Trump also attended a GOP dinner that night and basked in the applause of hundreds of dressed-to-the-nines attendees.

He spent Saturday golfing with singer-songwriter Kid Rock in temperatures that hit the 80s, and headed back to his golf club again on Sunday. Trump also spent time on the phone with trusted confidants.

The president's low-key approach was a marked shift from his posture in recent days. Beginning last weekend, he unleashed a storm of tweets that were unusually harsh and varied, even by Trump's standards.

He levelled fresh recriminations at the late Sen. John McCain. He called adviser Kellyanne Conway's husband a "loser husband from hell," former FBI Director James Comey a "dirty cop" and former Vice-President Joe Biden as a "low I.Q. individual." And Trump tweeted ongoing denouncements about the Mueller probe, saying it is the "biggest scandal in the history of the country."

Aides blamed that Twitter explosion in part due to too much free time. Heading into this high-stakes weekend, Trump advisers made a point of keeping the president busy and focused on positive developments, according to the Republican close to the White House.

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Riechmann reported from West Palm Beach, Florida. Lemire reported from New York. AP writers Darlene Superville and Jill Colvin contributed to this report.