During Sunday’s debate, Donald Trump once again said he doesn’t know whether Russia is trying to hack the U.S. election, despite Friday’s statement by the U.S. intelligence community pointing the finger at Putin –- and despite the fact that Trump was personally briefed on Russia’s role in the hacks by U.S. officials.

A senior U.S. intelligence official assured NBC News that cybersecurity and the Russian government’s attempts to interfere in the 2016 election have been briefed to, and discussed extensively with, both parties’ candidates, surrogates and leadership, since mid-August. "To profess not to know at this point is willful misrepresentation,” said the official. “The intelligence community has walked a very thin line in not taking sides, but both candidates have all the information they need to be crystal clear."

On Sunday, Trump disputed the idea there was any hack at all. “I notice, anytime anything wrong happens, they like to say the Russians are — [Hillary Clinton] doesn’t know if it’s the Russians doing the hacking. Maybe there is no hacking,” Trump told moderator Martha Raddatz of ABC News. “But they always blame Russia. And the reason they blame Russia because they think they’re trying to tarnish me with Russia. I know nothing about Russia.”

It’s the second time in two debates that Trump has declined to acknowledge that the hacks, mostly on Democratic targets, are real, much less that Russia is behind them.

“I don't think anybody knows it was Russia that broke into the DNC. She's saying Russia, Russia, Russia, but I don't -- maybe it was. I mean, it could be Russia, but it could also be China,” he told NBC’s Lester Holt on Sept. 26. “It could also be lots of other people. It also could be somebody sitting on their bed that weighs 400 pounds, OK?”

But weeks prior to the first debate, Trump had already been told privately by the intelligence community that the Russians were implicated.

On August 17, Trump got the first of the private briefings from U.S. intelligence officers to which he and Hillary Clinton are entitled as the major party presidential nominees.

As NBC News previously reported, classified materials prepared for the first briefing and examined by NBC News showed U.S. officials had drawn "direct links" between Vladimir Putin's government and the recent hacks and e-mail leaks.

“It’s common practice for all things in the briefing book to be used in the briefing,” said one U.S. official.

Since then, said an intelligence official, Trump and Clinton have had a second briefing, and their transition teams have received additional briefings on the Russian hack.

A little more than 48 hours before Sunday’s debate, the intelligence community and the Department of Homeland Security went public with their conclusion that the hack originated in the Kremlin, issuing a joint statement.

“The U.S. Intelligence Community (USIC) is confident that the Russian Government directed the recent compromises of e-mails from U.S. persons and institutions, including from U.S. political organizations.”

The statement added, “We believe, based on the scope and sensitivity of these efforts, that only Russia's senior-most officials could have authorized these activities.”