Updated at 11:55 a.m. with comments from Sen. Tim Kaine.

WASHINGTON — Of all the extraordinary moments in the final presidential debate, one that's been overshadowed was Donald Trump's rejection of the idea that Russia is behind a series of hacks aimed at swaying the election.

"She has no idea whether it's Russia, China, or anybody else," Trump insisted, after Hillary Clinton had noted that 17 U.S. intelligence agencies had blamed the Kremlin for directing the hacking.

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Trump's stance was particularly inexplicable because in a debate prep session Monday, one of his own national security advisers, House Homeland Security Committee Chairman Michael McCaul, told Trump that in his judgment — and that of the U.S. intelligence community — the hacks were directed by Russia.

House Homeland Security Committee Chairman Michael McCaul, R-Austin, says he told Donald Trump he believed the hacks were directed by Russia. (The Associated Press)

"I have personally briefed him on that and told him that in my opinion ... this was in fact a nation-state attack by Russia," McCaul said Wednesday.

Hours later on the Las Vegas debate stage, Clinton cornered Trump on the topic, calculating correctly that he would dig in and persist in his refusal to accept the judgment of the nation's top intelligence officials.

"This has come from the highest levels of the Russian government, clearly, from [Vladimir] Putin himself, in an effort, as 17 of our intelligence agencies have confirmed, to influence our election," she said.

"Will Donald Trump admit and condemn that the Russians are doing this and make it clear that he will not have the help of Putin in this election, that he rejects Russian espionage against Americans, which he actually encouraged in the past?" Clinton said.

The exchange may be better remembered for the bickering, in which she and Trump accused each other of being "a puppet" for Putin.

"This is such an unprecedented situation," she added. "We've never had a foreign government trying to interfere in our election. We have 17 intelligence agencies, civilian and military, who have all concluded that these espionage attacks, these cyberattacks, come from the highest levels of the Kremlin and they are designed to influence our election."

Trump dug in.

"She has no idea," he said. "Hillary, you have no idea. And our country has no idea."

Clinton was talking over Trump at this point, saying she wasn't quoting herself but the nation's intelligence agencies.

"Yeah, I doubt it. I doubt it," Trump said.

Fox News' Chris Wallace, the debate moderator, reinforced reality and Clinton's version of it moments later, after Trump had pivoted to an attack on Clinton's weakness on foreign policy.

"The top national security officials of this country do believe that Russia has been behind these hacks. Even if you don't know for sure whether they are, do you condemn any interference by Russia in the American election?" Wallace asked.

"By Russia or anybody else," Trump said. "Of course I condemn."

The GOP nominee's insistence on substituting his own judgment for that of the nation's military and civilian security agencies was remarkable.

On Thursday, Clinton's running mate, Sen. Tim Kaine of Virginia, used Trump's stance on the hacks as evidence of his unfitness.

"Donald Trump has received the same briefings that I have received," he said while stumping Thursday in Charlotte, N.C. "He has been told that by our top security professionals. ... This is surreal, folks."

If Trump wins, and McCaul does land a Cabinet spot as he's said he'd like, he'll have to find ways to be more persuasive, because this boss doesn't readily accept input.