Obama's comments reflected Democratic efforts to frame the election not just as a choice between party philosophies but as a crucial moment in American democracy. The president suggested Trump was trying to discredit the electoral process rather than campaign on his ideas and accept the verdict of the voters.
Speaking to reporters at the White House, Obama mocked Trump for complaining, while the race is still afoot, that the vote count might be fixed.
"If 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 said, his voice cracking with amusement.
"I'd invite Mr. Trump to stop whining and go try to make his case to get votes," he added.
Though taking on the popular sitting president would be an unconventional strategy at this point, Trump has proved that he is susceptible to provocation, and Obama seemed to be aiming straight for that vulnerability.
Trump, whose disdain for Obama dates back to his amplification of the so-called birther movement that tried to delegitimize Obama's presidency, publicly held his fire. He referred to Obama only generally at a rally in Colorado.
But a more significant rejoinder appeared to be in the works; he planned to invite Obama's estranged half-brother as his guest to Wednesday's final presidential debate, a campaign aide said.
Malik Obama, a few years older than the president, is the son of Obama's father and a different wife. He has met the president a few times, but the two are not close. He has told reporters in recent weeks that he supports Trump for president.
For Trump, the prolonged silence was a departure. He has repeatedly responded to criticism by firing in anger, fueling Democratic nominee
Trump feuded with Fox News anchor Megyn Kelly after she questioned him harshly during the first GOP primary debate last year, and he spent days complaining after the parents of an Army captain killed in Iraq criticized him this summer.
And after the first presidential debate with Clinton, as Trump attacked a former Miss Universe whom he had publicly shamed for gaining weight, supporters began steadily abandoning him, polls show.
Obama's direct jab at Trump was the latest alarm sounded by Democrats as Trump levels charges of a vast conspiracy to rob him of electoral victory.
Trump is "trying to distract from the bad story line of his verbal and physical assaults on women," said senior Clinton advisor Jennifer Palmieri. "And because he's losing and he wants to blame somebody else — and that's what losers do."
Standing alongside Italian Prime Minister Matteo Renzi, Obama vowed to be more “subdued” talking about the
He mocked Trump for his “flattery” of Russian President
Then he turned to Trump's complaints of a "rigged system," suggesting that Trump is discrediting the election process rather than trying to sell his ideas to voters.
"It happens to be based on no facts," he said. Serious analysts, he said, "will tell you that instances of significant voter fraud are not to be found."
Generations of defeated presidential candidates in the U.S. have conceded to their winners and participated in a peaceful transfer of power, Obama said.
"Democracy by definition works by consent," Obama said. What Trump is doing, he said, "is unprecedented."
Trump's protests fail to show "the kind of leadership and toughness" voters want in a president, Obama said.
The official visit of the Italian prime minister for a state dinner, the 13th and final of Obama's presidency, was replete with allusions to the unusual presidential contest.
As he formally welcomed Renzi to the White House, Obama noted that "America was built by immigrants. America is stronger because of immigrants," he said.
Renzi spoke of building "bridges, not walls," an indirect reference to Trump's call to build a wall along the border with Mexico. And he said Italians were more interested in the American presidential election than in their own upcoming constitutional referendum.
But the attention was on Obama's parry with Trump.
Obama has proved to be more able than anyone to provoke Trump, said Paul Begala, a Democratic strategist.
"He taunts and baits Trump; he ridicules and humiliates him. And then, just to show us all how it's done, he takes the whole absurd circus and contextualizes it, reminding us that the person who occupies the Oval Office has the power to destroy all life on earth — something not to be trifled with. He is conducting a master class on how to take on a bully."
Times staff writers Noah Bierman in Grand Junction, Colo., and Evan Halper aboard the Clinton campaign plane contributed to this report.
5 p.m.: This story was updated with more comments from Obama and background on Trump.