US Special Counsel Robert Mueller's conclusion that Donald Trump did not collude with Russia to win the US presidency in 2016 gave Trump a powerful weapon to use against his Democratic opponents and a potential boost to what is shaping up to be a tough bid for re-election in 2020. On Sunday, US Attorney General William Barr sent a four-page summary of the Mueller report to lawmakers, highlighting the finding that neither Trump nor any of his close aides conspired with Russia to defeat his Democratic opponent, Hillary Clinton. But the probe left unresolved the question of whether Trump engaged in obstruction of justice, setting out “evidence on both sides of the question”. Trump and his supporters, who celebrated the report as an end of a “witch hunt” by Democrats, ignored the shadows of doubt on the “obstruction of justice” charge, especially as Barr stated he found no grounds to sue the president after being cleared from the main accusation: collusion with Russia. Mueller's decision to clear Trump took away a central charge that Democrats have flung at Trump for two years — that he did not win the presidency fairly. Democrats have vowed to continue congressional investigations into the 2016 election campaign and Trump's business practices. But without the solid foundation of evidence of any crimes by the president, they now risk seeming to overplay their hand. “This is a gold star day for Donald Trump,” said presidential historian Douglas Brinkley. “Now the shackles are off. He's able to demonise the news media and Democrats as perpetuating what he calls a hoax. And he'll be able to use his innocence as fodder for the campaign trail.” The question for Trump now is whether he will be able to bring a minimum of discipline to his campaign messaging and to the presidency itself. Just last week, he was immersed in a strange fight with a dead man, sharply criticising late Republican Senator John McCain and falsely accusing him of being at the root of some of the collusion allegations against him. He has also been prone to making baffling and abrupt decisions, such as occurred last week when he called off a round of sanctions against North Korea before they had even been imposed. Despite the Mueller report conclusions, Trump remains an intemperate president, eager to lash out at any and all critics. “This was an illegal takedown that failed,” Trump said Sunday, even though Mueller left open the question of obstruction. Speaking to reporters before boarding Air Force One for Washington, Trump called for Democrats to be investigated, expanding on his oft-repeated assertion that the Mueller probe was Democrat-inspired. Mueller was appointed by Trump's Department of Justice in 2017 after he fired FBI director James Comey. “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 said. “Before I even got elected it began, and it began illegally.” Trump attempted to strike a more moderate tone Monday, saying Mueller acted honourably in conducting the Russia investigation while complaining about a “false narrative” and people who have done unspecified “treasonous” things. “We're glad it's over. It's 100 per cent the way it should have been,” Trump told reporters at the White House while sitting next to Israeli Prime Minister Binyamin Netanyahu. “I wish it could have gone a lot sooner, a lot quicker. There are a lot of people out there that have done some very, very evil things, very bad things, I would say treasonous things against our country. “Hopefully... people who have done such harm to our country... those people will certainly be looked at,” Trump said, citing people he said have lied to Congress. Trump supporters viewed the Mueller report as a blow to the more than a dozen Democrats who are campaigning for their party's 2020 presidential nomination. “This is very problematic for any Democrat who's running for president in 2020 that was hoping they would face a weakened or beaten-down President Trump,” former Trump campaign adviser Jason Miller said. “In fact, President Trump will likely see a ratings boost coming out of this and a strong tailwind pushing him towards the upcoming election.” Despite the undeniable Trump victory, Democratic lawmakers said it was early to celebrate, and vowed to continue pressing several other investigations into Trump's tax records, and so-called “hush money” his former lawyer paid to two porn actresses in order not to reveal details on affairs with the president before elected. After Barr concluded there was insufficient evidence to bring an obstruction case against Trump, Democratic lawmakers are now calling for the release of the full report and the underlying evidence Mueller relied on. House of Representatives Judiciary Committee Chairman Jerrold Nadler, a Democrat, said on CNN Sunday he would “try to negotiate” with the Justice Department to obtain the full report, but that the committee would issue subpoenas and litigate if needed. Other Democrats, including candidates vying for the 2020 presidential nomination, have called for release of the full report. The Justice Department has not said whether it will release Mueller's full report, but Barr has said he will be as transparent as possible. Barr could also keep parts of the report under wraps by invoking a Justice Department policy against disparaging individuals who have not been charged with crimes. The most contentious fight will likely be over any materials the White House tries to shield from public view by claiming executive privilege, a legal doctrine generally used to keep conversations between the president and advisers private. The doctrine is rooted in the idea that the president should be able to receive candid advice on policy matters.