In language normally reserved for chastising a stroppy teenager, Obama discarded diplomatic decorum and skewered the mogul from the Rose Garden in front of visiting Italian Prime Minister Matteo Renzi.
As Trump’s poll numbers have been dragged down by accusations of sexual assault, he has unfurled a litany of complaints about the nation’s election system.
Democrat Hillary Clinton has widened her lead over Trump nationally and in key swing states three weeks before Election Day.
Bookmakers in Europe — where political betting is legal — have already begun to pay out on a Clinton win.
“Of course there is large scale voter fraud happening on and before election day,” Trump wrote on Twitter, without offering corroborating evidence.
Obama shot back: “There’s no evidence that that has happened in the past, or that there are instances in which that will happen this time.”
“And so I’d advise Mr Trump to stop whining and go try to make his case to get votes,” he told a news conference.
The withering riposte comes on the eve of the third and final presidential debate, and is just the type of comment that has baited Trump into launching distracting Twitter feuds and campaign speech tangents.
Obama also renewed his effort to tether Republicans to Trump’s faltering candidacy and described his behaviour as an aberration in American democratic history.
“I have never seen in my lifetime or in modern political history any presidential candidate trying to discredit the elections and the election process before votes have even taken place.
It’s unprecedented,” Obama said.
“That is both irresponsible — and, by the way, it doesn’t really show the kind of leadership and toughness that you’d want out of a president.
You start whining before the game’s even over?”
“If whenever things are going badly for you and you lose you start blaming somebody else, then you don’t have what it takes to be in this job.”
Obama also slammed Trump’s “flattery” of Russia’s Vladimir Putin as “unprecedented” and “out of step” with both Democrats and rank-and-file Republicans.
The Republican presidential nominee has repeatedly voiced admiration for the Russian president — notably calling him a better leader than Obama — and advocated a US rapprochement with Moscow.
Trump’s support for Russia comes at a time of escalating tensions, as Washington and Moscow lock horns over the Syria conflict, and US officials accuse Russia of directing cyber attacks aimed at interfering in November’s election.
Obama said he was troubled that other Republicans were supporting the Republican presidential candidate’s positions on Russia.
Saying “Mr. Trump rarely surprises me these days,” Obama said he was much more concerned to see support for the candidate’s stance on Putin and Russia from Republican officials who historically had been anti-Russia.
Historically, Republican politicians have often taken or appeared to take a harder line on Russia’s predecessor, the Soviet Union, the US’ Cold War foe.
Obama said Russia’s behaviour has undermined international norms and said any suggestion that the United States has encroached on Russian interests is wrong.
“We think that Russia is a large, important country with a military that is second only to ours and has to be a part of the solution on the world stage rather than part of the problem,” Obama said.
“But their behavior has undermined international norms and international rules in ways we have to call them out on,” Obama said, citing “Russian aggression in Ukraine” and other actions.
Russia has been internationally condemned for its 2014 annexation of Crimea from Ukraine and its support of pro-Russian separatists in eastern Ukraine.
The US state department is denying that it sought to influence the FBI to change a security classification on one of Hillary Clinton’s e-mails.
Documents newly released by the FBI under the Freedom of Information Act cite one official from the law enforcement agency who believed there was a “quid pro quo” suggested by a high-ranking state department official.
The documents are part of the FBI’s investigation into the use of a private email server by Clinton, the Democratic presidential nominee, when she was secretary of state from 2009-13.
Her emails have been a persistent issue in the campaign, reinforcing perceptions of Clinton as flouting rules for personal expedience.
The summary of an interview with an unnamed FBI official described his belief that a “quid pro quo” was offered by Patrick Kennedy, undersecretary of state for management, to a second FBI official.
The FBI had been seeking permission from the state department to station more agents in Iraq, and Kennedy was described as trying to convince the FBI to change its ruling to classify one of Clinton’s 55,000 e-mails.
“Our view is... that there was no quid pro quo even suggested,” State department spokesman John Kirby told broadcaster MSNBC.
“There were two conversations. One about the fact that we disagreed with this e-mail being classified as secret.... Those conversations were happening at the same time, but they were not linked. There was no bargain suggested here.”
The FBI ultimately did not reclassify the email in question, Kirby pointed out.
Young Americans are so dissatisfied with their choices in this presidential election that nearly one in four told an opinion poll they would rather have a giant meteor destroy the Earth than see Donald Trump or Hillary Clinton in the White House.
The tongue-in-cheek question was intended to gauge young Americans’ level of unhappiness about their choices in the November 8 election, said Joshua Dyck, co-director of UMass Lowell’s Center for Public Opinion, which conducted the poll alongside Odyssey Millennials.
The choice alluded to the Twitter hashtag “#GiantMeteor2016,” a reference to an imaginary presidential candidate used to express frustration about this year’s election choices.
Some 53% of the 1,247 people aged 18 to 35 said they would prefer to see a meteor destroy the world than have Republican New York real estate developer Trump in the Oval Office, with some 34% preferring planetary annihilation to seeing the Democratic former Secretary of State win.
Some 39% said they would prefer that US president Barack Obama declare himself president for life than hand over power to Clinton or Trump, with 26% saying the nation would do better to select its next leader in a random lottery.
Some 23%, nearly one in four, preferred the giant meteor outcome to either Trump or Clinton.
“Obviously we don’t think that they’re serious,” Dyck said in a phone interview on Tuesday.”The fact that one in four of our young people pick ‘Giant Meteor’ tells you something about the political disaffection that is being shown by American youth.”
That contrasts with the surge of participation by young voters that helped propel Obama into the White House for his first term in the 2008 election.
When asked to choose between the actual candidates, Clinton easily led Trump with 54 % of respondents to 21 % in a two-way race.
In a four-way race also including Libertarian Gary Johnson and Green Party candidate Jill Stein, Clinton led with 48 % support, to Trump’s 20 %, Johnson’s 10 % and Stein’s 4 %. In national polls surveying the whole population, Clinton is leading Trump, but not by nearly as much.
