WASHINGTON • United States Attorney-General William Barr has handed Mr Donald Trump the biggest political victory of his presidency with an assessment that there was no collusion with Russia during the 2016 election campaign and there was not enough evidence to find that he obstructed justice.

Mr Trump celebrated Sunday's news with relish, tweeting "Complete and Total EXONERATION", and telling reporters that Special Counsel Robert Mueller's 22-month inquiry into Russian interference was "an illegal takedown that failed".

"It is a shame that the country had to go through this," said Mr Trump.

It was the close of a politically explosive investigation that Mr Trump routinely dismissed as a "witch hunt". The finding on collusion between Russia and the Trump campaign was unambiguous.

"The Special Counsel did not find that the Trump campaign, or anyone associated with it, conspired or coordinated with the Russian government in these efforts, despite multiple offers from Russian-affiliated individuals to assist the Trump campaign," Mr Barr said in a four-page letter to Congress on Sunday.

But the determination on whether Mr Trump sought to obstruct justice was less clear cut.

Mr Mueller's still-secret "report found evidence on both sides of the question" concerning obstruction, and "leaves unresolved what the Special Counsel views as difficult issues of law", Mr Barr wrote.

He quoted Mr Mueller as saying that "while this report does not conclude that the President committed a crime, it also does not exonerate him".

Mr Barr also said there were no new surprises coming from the Mueller team - which is disbanding - in the form of further indictments, and with no sealed indictments outstanding.

Deputy press secretary Hogan Gidley said Mr Trump was "in a really good mood" and "very happy with how it all turned out".

Some Trump allies said the outcome amounted to vindication, much like their victory on election night in 2016, with Mr Trump once again overcoming what they regard as an attempt by Democrats to stop him.

Mr Barr's letter also alleviated some fear among Trump's aides that Mr Mueller's findings would give Democrats solid ammunition to seek the President's impeachment. The White House was not involved in any review or discussion of the Mueller report and did not get a look at Mr Barr's summary ahead of time, according to a Justice Department official.

Before completing his probe, Mr Mueller helped secure guilty pleas from five people involved in Mr Trump's presidential campaign - including his campaign chairman Paul Manafort and Michael Flynn, who became his first national security adviser - though none admitted to conspiring with Russian operatives.

He also indicted more than two dozen Russian hackers and military intelligence officers.

The political fight over Mr Mueller's findings is far from over, with top Democrats demanding the release of his complete report - and all the evidence he compiled - and threatening a subpoena fight that could end up in the Supreme Court.

"It is unacceptable that, after Special Counsel Mueller spent 22 months meticulously uncovering this evidence, Attorney-General Barr made a decision not to charge the President in under 48 hours," the Democratic chairs of the House Judiciary, Intelligence and Oversight committees said in a joint statement. "His unsolicited, open memorandum to the Department of Justice, suggesting that the obstruction investigation was 'fatally misconceived', calls into question his objectivity on this point in particular."

Retired Ford assembly plant worker and Trump supporter Henry Thompson was giddy as he listened to a summary of Mr Mueller's Russia report on TV at a Dearborn, Michigan, diner on Sunday . "Finally, we get to stick it to all the haters who want to undermine our President," said Mr Thompson, a lifelong Democrat who backed Mr Trump in the 2016 campaign for his opposition to the North American Free Trade Agreement.

"How many times did Trump say, 'No collusion', and he was right. They say the President lies. But his enemies have lied about this from the beginning," he said.

With the probe concluded, Russia urged Mr Trump to seize the opportunity to reset relations.

"There is a chance to renew much in our relations, but the question is whether Trump will take the risk," Mr Konstantin Kosachyov, chairman of the International Relations Committee in Russia's Upper House of Parliament, wrote yesterday on Facebook.

A Kremlin spokesman said there was no validity to continued accusations that Russia meddled in the US election campaign.

BLOOMBERG, AGENCE FRANCE-PRESSE, REUTERS