Obama all-but accused Russian President Vladimir Putin of personally ordering an audacious cyber hack that many Democrats believe gravely wounded Hillary Clinton in a closely fought election.
The US intelligence community has concluded that a hack-and-release of the Democratic Party emails was designed to put Trump -- a political neophyte who has praised Putin -- into the Oval Office.
But with tensions rising between the world's two preeminent nuclear powers and US political anger near boiling point after Trump's shock election, Obama sought to exude calm while promising a measured response.
Assuring Americans that the ballot itself was not rigged, he promised to "send a clear message to Russia or others not to do this to us, because we can do stuff to you."
Noting that "not much happens in Russia without Vladimir Putin," Obama said he had personally told the former KGB officer when they met in September to "cut it out."
"In fact we did not see further tampering of the election process," he told journalists before heading for his Christmas vacation in Hawaii.
Regarding specific acts of retaliation, Obama said some would be carried out publicly, but that in other cases, "the message will be directly received by the Russians and not publicized."
Obama's comments come as Putin registered a major propaganda victory in Syria and became a focal point of American political debate.
Despite those coups, Obama belittled Russia as a second rate power with little going for it, using language that is sure to infuriate the status-conscious Russian leader.
"The Russians can't change us or significantly weaken us. They are a smaller country, they are a weaker country, their economy doesn't produce anything that anybody wants to buy except oil and gas and arms. They don't innovate."
But Obama's sternest message may have been for Trump and other Republicans who have played down the cyber attack.
"Over a third of Republican voters approve of Vladimir Putin," Obama said citing a recent poll. "Ronald Reagan would roll over in his grave. How did that happen?"
Obama urged the president elect -- who has repeatedly questioned Russia's involvement -- to accept an independent nonpartisan investigation.
"My hope is that the president-elect is going to similarly be concerned with making sure that we don't have potential foreign influence in our election process."
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While Obama has ordered his own inquiry, a political battle is already being waged in Washington between Republicans who want a Congressional process they can control and Democrats who want to see something like the bipartisan 9/11 Commission.
"One way I do believe the president-elect can approach this that would be unifying is to say that we welcome a bipartisan, independent process," Obama said.
The outgoing president also issued his fiercest warning shot for the president-elect about embracing illiberal politics.
"Mr. Putin can weaken us just like he's trying to weaken Europe if we start buying into notions that it's okay to intimidate the press. Or lock up dissidents. Or discriminate against people because of their faith or what they look like."
Republicans were unimpressed by Obama's efforts to dial back tensions with Senator Ben Sasse accusing Obama of a "mere scolding of dictators."
"Instead of President Obama's vague 'we can do stuff,' Congress should debate upending Putin's calculus with a full menu of diplomatic, economic, military, and cyber responses."
Clinton slams Putin
Hillary Clinton blames Russian President Vladimir Putin, who had a "personal beef" against her, and a late-hour FBI intervention over her email scandal for her loss to Donald Trump in the US election, a newspaper reported Friday.
Clinton, 69, has kept a low profile in the weeks since her shock defeat to the Republican billionaire, but made the remarks to campaign donors in Manhattan on Thursday night, The New York Times reported.
The Democratic former secretary of state won the popular vote by more than 2.7 million ballots but lost the crucial Electoral College by 232 to 306.
Trump walked away with the election because he won a string of swing states. Crucially his wins in three of those states, Wisconsin, Pennsylvania and Michigan, amounted to a combined total of around 100,000 votes.
The Times said Clinton told donors that a letter from FBI director James Comey revisiting her private server scandal dating back to her time as secretary of state, 10 days before the election, cost her close races in several states.
"Swing-state voters made their decisions in the final days breaking against me because of the FBI letter from Director Comey," the Times quoted her as saying.
She said the hacking of the Democratic National Committee (DNC) and her campaign chairman John Podesta's emails stemmed from Putin's "personal beef" against her, the newspaper reported.
Clinton said the reason was her accusation that Russia's 2011 parliamentary elections were rigged.
"Putin publicly blamed me for the outpouring of outrage by his own people, and that is the direct line between what he said back then and what he did in this election," the Times quoted her as saying.
On Thursday, Podesta lashed out at the FBI in a scathing op-ed published in The Washington Post, slamming the Federal Bureau of Investigation for its "failure" to adequately respond to the Democratic Party email hacks.
An investigation published by the Times earlier this week said that when the FBI discovered the hack in September 2015, it left phone messages with the DNC "help desk" but did not warn senior Democratic officials or visit in person.
"Comparing the FBI's massive response to the overblown email scandal with the seemingly lackadaisical response to the very real Russian plot to subvert a national election shows that something is deeply broken at the FBI," he wrote.
In the immediate aftermath of the election, however, some Democrats including advisers close to her husband, former president Bill Clinton, directed blame at Clinton's own campaign.
The campaign reportedly ignored calls from Bill Clinton to spend more time focusing on disaffected white, working class voters -- a key demographic that elected Bill Clinton twice and backed Trump.
Clinton did not visit Wisconsin as the Democratic nominee and only pushed late into Michigan after polls showed the race tightening.