Trump, who has expressed skepticism over the findings, received a private briefing on the report from US officials Friday in NY.
But after meeting with the intelligence officials, Trump appeared to moderate his position, conceding that "Russia, China, other countries, outside groups and people are consistently trying to break through the cyberinfrastructure of our governmental institutions, businesses and organizations, including the Democrat National Committee".
In tweets this week, Trump ridiculed the Central Intelligence Agency and Federal Bureau of Investigation conclusions, which are supported by outgoing President Barack Obama, that hackers working at the bidding of the Russian government stole embarrassing Democratic Party documents from the party's computers and leaked the via WikiLeaks to undermine the presidential campaign of Trump rival Hillary Clinton.
Referring to a planned presentation to him by intelligence chiefs, Trump tweeted: "The "Intelligence" briefing on so-called "Russian hacking" was delayed until Friday, perhaps more time needed to build a case".
Clapper said there were "multiple motives" by Russian Federation for hacking during the campaign. "There were attempts to hack the Republican National Committee, but the RNC had strong hacking defenses and the hackers were unsuccessful". The president-elect maintained that possible Russian actions had no effect on the election.
Nunes added that the president-elect is surrounding himself with people who understand the "Russia threat".
"There are a variety of different exhibits that make the case, different factors that have provided the intelligence community with high confidence" that Russian Federation sought in part to help elect Trump, said a second senior US official who has reviewed intelligence findings on Russia's cyber operations.
Immediately after the November 8 election, Russian Federation began a "spear-phishing" campaign to try to trick people into revealing their email passwords, targeting USA government employees and think-tanks that specialize in national security, defence and foreign policy, the unclassified version of the report said.
Priebus also said the DNC and Clinton campaign chairman John Podesta must share the blame for being hacked, alleging that neither had adequate security to prevent the Russians from gaining access to their systems.
He then added to the insult by citing WikiLeaks founder Julian Assange in his dismissal of the findings of multiple USA agencies that Russian Federation was behind the hacking.
"This document's conclusions are identical to the highly classified assessment, but this document does not include the full supporting information, including specific intelligence on key elements of the influence campaign", the report said.
Russia's state-sponsored English-language TV network RT also repeatedly slammed Clinton and praised Trump in its programming, the report said.
The British role, which has been closely held, is a critical part of the timeline because it suggested that some of the first tip-offs, in fall 2015, came from voice intercepts, computer traffic or informants outside the United States, as e-mails and other data from the Democratic National Committee flowed out of the country.
Obama said he takes "some responsibility" for the Democratic Party's losses during his two terms among House and Senate members and in state legislatures.