US spy chiefs insisted today they have strong evidence that Russia mounted an unprecedented bid to disrupt the American election, standing firm in the face of Donald Trump's refusal to accept their conclusions.
One day before the heads of four intelligence bodies brief the president-elect on their assessment of Russian meddling in last year's race, Director of National Intelligence James Clapper told a Senate hearing he had "very high" confidence in their findings.
"The Russians have a long history of interfering in elections, theirs and other people's," he told the Armed Services Committee. "But we have never encountered such a direct campaign to interfere with the election process as we have seen in this case."
"This was a multifaceted campaign. So the hacking was only one part of it, and it also entailed classical propaganda, disinformation, fake news," Clapper said.
Clapper, National Security Agency chief Michael Rogers and Marcel Lettre, undersecretary of defense for intelligence, told the committee in a joint statement that "only Russia's senior-most officials" could have authorised the operation, in which hackers stole Democratic Party files and emails, which were then disseminated via WikiLeaks, embarrassing the party and harming losing candidate Hillary Clinton's White House effort.
"Russia has clearly assumed an even more aggressive cyber posture by increasing cyber espionage operations, leaking data stolen from these operations and targeting critical infrastructure systems," Clapper said.
Trump, who has pledged to bring about a rapprochement with President Vladimir Putin's Russia after taking office on January 20, has repeatedly dismissed that finding.
The Republican president-elect has mocked via Twitter past intelligence errors of the CIA, FBI and other agencies, challenging them to prove that the hacking and leaks could be traced up to the top of Putin's government.
Today's much-anticipated hearing, which came ahead of the expected release early next week of a comprehensive White House report on Russian election interference, did not offer any new evidence.
When asked by senators to provide more proof, Clapper repeatedly said he could not do so in public, saying it risked damaging the intelligence community's sources and operations.
"We have invested billions, and we have put people's lives at a risk to glean such information," he said.
Trump will be briefed tomorrow by Clapper, Rogers, Federal Bureau of Investigation director James Comey and Central Intelligence Agency Director John Brennan on the details of the report, amid concerns Trump has already soured relations with key parts of his national security establishment.
Asked if the report will ascribe a motive to Putin for allegedly ordering the campaign, Clapper replied: "Yes, we will ascribe motivation.