Hours before he was to receive a top secret briefing from senior U.S. officials about Russian actions involving the 2016 elections, President-Elect Donald Trump again publicly questioned the findings of the Intelligence Community, once more charging that politics was at play more than anything else.

"So how and why are they so sure about hacking," Trump wrote in a series of tweets, as he expressed frustration about press reports indicating that U.S. officials still believe Russia - and its top leaders were to blame.

The Trump tweets came after a Senate hearing earlier in the day where intelligence officials made clear that hack of the Democratic National Committee, as well as the email hack of a top aide to Hillary Clinton, could be laid at the feet of Russian intelligence, a charge that Trump has long questioned.

"This was actually part of a multifaceted campaign that the Russians mounted," said Director of National Intelligence James Clapper, who accused Russia of not only hacking, but using propaganda, disinformation and fake news to try to undermine the 2016 election for President.

"The hacking was only one part of it," Clapper told Senators.

At the hearing, Clapper and other officials were asked several times about public push back by Trump and his supporters on the issue of Russian election meddling.

Clapper said he was ready to lay out all the facts to President-Elect Trump on Friday.

Clapper will go to New York on Friday to brief Mr. Trump, along with FBI Director James Comey, NSA chief Admiral Michael Rogers and CIA Director John Brennan.