Donald Trump Casts Doubt on Intelligence Community Over 'So-Called' Russian Hacking

— -- Donald Trump continues to remain indignant about claims that Russia is responsible for cyberassaults on the U.S., taking to Twitter Tuesday night to reiterate his skepticism.

In a single tweet, Trump questioned the prevailing notion that Russia has been hacking U.S. entities — despite 17 U.S. intelligence agencies concluding that top Russian officials helped orchestrate cyberattacks against the Democratic National Committee and members of Hillary Clinton's campaign — and he also seemed to question the validity of such agencies overall.

The president-elect tweeted, "The 'Intelligence' briefing on so-called 'Russian hacking' was delayed until Friday, perhaps more time needed to build a case. Very strange!"

While the basis of Trump's tweet is that the intelligence briefing was slated for Tuesday and bumped to Friday, a source familiar with the matter tells ABC News that the briefing had always been slated for Friday.

Last week a 13-page report from the FBI and the Department of Homeland Security linked the Russian government to hacks of Democratic organizations

Trump's skepticism is nothing new. On New Year's Eve he expressed a lack of confidence in intelligence officials' findings.

"Well, I just want them to be sure, because it's a pretty serious charge, and I want them to be sure. And if you look at the weapons of mass destruction, that was a disaster, and they were wrong," Trump said, when asked why he seems to doubt the intelligence analysis that Russia is behind the hacking, referring to the intelligence cited about Iraq possessing weapons of mass destruction leading up to the Iraq War.

"And so I want them to be sure. I think it's unfair if they don't know," he added. "And I know a lot about hacking. And hacking is a very hard thing to prove. So it could be somebody else. And I also know things that other people don't know, and so they cannot be sure of the situation."

ABC News' Katherine Faulders and Mike Levine contributed to this report.