Washington (CNN) The leading US intelligence official said Thursday that his foreign counterparts have expressed concern that President-elect Donald Trump is disparaging the US intelligence community, potentially damaging public confidence.

"I do think public trust and confidence in the Intelligence Community is crucial" both in the US and in other countries that rely on US intelligence, James Clapper, the Director of National Intelligence, told the Senate Armed Services Committee. "I've received many expressions of concern from foreign counterparts about the disparagement of the US Intelligence Community, or I should say, what has been interpreted as disparagement of the US Intelligence Community."

Clapper was speaking at a hearing on global cyberthreats that focused almost exclusively on Moscow's alleged hacking during the presidential elections.

The hearing gave lawmakers and senior US intelligence officials the chance to draw a line in the sand for Trump, presenting a united front on their conclusion that Russia is a major threat to the United States and was behind election-related hacking -- a conclusion the President-elect has refused to accept.

"We assess that only Russia's senior-most officials could have authorized the recent election-focused data thefts and disclosures, based on the scope and sensitivity of the targets," Clapper, Undersecretary of Defense for Intelligence Marcel Lettre and the commander of US Cyber Command, Michael Rogers, wrote in a joint statement to the Senate Armed Services Committee.

Clapper said at the hearing that there was a line between critical thinking about assessment and undermining those gathering the intelligence.

"I think there is an important distinction here between healthy skepticism which policymakers -- to include policymaker No. 1 -- should always have on intelligence, but I think there's a difference between skepticism and disparagement," he said.

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And he noted that some intelligence agents die in service for their country. "You only need to walk into the lobby and look at the stars on the wall or the NSA and the number of intelligence people who have paid the ultimate price for their country," he said.

Rogers told the committee that he was concerned about morale within the Intelligence Community and that having political leaders who are confident in intelligence agencies is "crucial to that."

"I don't want to lose good, motivated people because they feel there's not room for them to contribute," Rogers said. "Without that confidence, I just don't want a situation where our workforce decides to walk because that's just not a good place for us to be."

Sen. Lindsey Graham, a South Carolina Republican, said he wanted to convey to Trump that "It's okay to challenge the intel, you're right to do so, but what I don't want you to do is undermine those who are serving our nation in this arena until you're absolutely sure they need to be undermined.

"And I think they need to be uplifted," Graham added, "not undermined."

In his opening questions to Clapper, Committee Chairman John McCain noted the Intelligence Community's conclusion that the cyberthefts and disclosures were intended to interfere with the US election process and could only have been authorized by Russia's most senior levels.

"We stand actually more resolutely on the strength of that statement that we made on the seventh of October," Clapper said. After the election, the Intelligence Community concluded that at least one Russian motive had been to help Trump win.

Clapper said that the hacking did not succeed in changing any vote tallies, but that it was impossible for intelligence to assess how the information released from the breaches affected voters' attitudes.

McCain emphasized the Russian role and delivered an implicit rebuke to Trump, who has urged people to "move on" from the issue of Moscow-directed hacking.

"Every American should be alarmed by Russia's attacks on our nation," the Arizona Republican said. "There's no escaping the fact that this committee meets today ... in the aftermath of an unprecedented attack on our democracy."

McCain added that the "goal of this review is not to question the outcome of the election nor should it be." It's crucial that the country move forward with full knowledge about what happened and that Congress take bipartrisan steps, he said.

Russia reacted almost immediately, with Kremlin spokesman Dmitr Peskov telling CNN that Moscow is "sick and tired of those irresponsibly blaming everything on our country. If there is a need for an enemy, why not to try someone else?"

"We have suggested cooperation on combating cyberthreats numerous times," Peskov said. "It was rejected."

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But both Clapper and Rogers said in their testimony that the US has been trying to create international norms for cyber-related conflict. "We continue to engage with partners around the world about what is acceptable and unacceptable behavior in cyberspace, " Rogers said. "We are clearly not where we want to be in this regard."

Trump has suggested that the Intelligence Community's conclusion on Russia was driven by political interests. Clapper, who enlisted in the Marine Corps in 1961, stressed that he has served every president "in the trenches" since John F. Kennedy.

"I am apolitical," he said, adding that it was a priority to supply "unvarnished" and "untainted" policy recommendations to policy makers.

Photos: WikiLeaks founder Julian Assange Photos: WikiLeaks founder Julian Assange WikiLeaks founder Julian Assange speaks to the media from the balcony of the Ecuadorian Embassy in London in May 2017. Assange, founder of the website WikiLeaks, has been a key figure in major leaks of classified government documents, cables and videos. Hide Caption 1 of 22 Photos: WikiLeaks founder Julian Assange Assange holds a copy of The Guardian newspaper in London on July 26, 2010, a day after WikiLeaks posted more than 90,000 classified documents related to the Afghanistan War. Hide Caption 2 of 22 Photos: WikiLeaks founder Julian Assange Assange attends a seminar at the Swedish Trade Union Confederation in Stockholm on August 14, 2010. Six days later, Swedish prosecutors issued a warrant for his arrest based on allegations of sexual assault from two women. Assange has always denied wrongdoing. Hide Caption 3 of 22 Photos: WikiLeaks founder Julian Assange Assange, in London, displays a page from WikiLeaks on October 23, 2010. The day before, WikiLeaks released approximately 400,000 classified military documents from the Iraq War. Hide Caption 4 of 22 Photos: WikiLeaks founder Julian Assange Assange and his bodyguards are seen after a news conference in Geneva, Switzerland, in November 2010. It was the month WikiLeaks began releasing diplomatic cables from US embassies. Hide Caption 5 of 22 Photos: WikiLeaks founder Julian Assange Assange sits behind the tinted window of a police vehicle in London on December 14, 2010. Assange had turned himself in to London authorities on December 7 and was released on bail and put on house arrest on December 16. In February 2011, a judge ruled in support of Assange's extradition to Sweden. Assange's lawyers filed an appeal. Hide Caption 6 of 22 Photos: WikiLeaks founder Julian Assange In October 2011, a month after WikiLeaks released more than 250,000 US diplomatic cables, Assange speaks to demonstrators from the steps of St. Paul's Cathedral in London. Hide Caption 7 of 22 Photos: WikiLeaks founder Julian Assange Assange leaves the High Court in London in December 2011. He was taking his extradition case to the British Supreme Court. Hide Caption 8 of 22 Photos: WikiLeaks founder Julian Assange Assange leaves the Supreme Court in February 2012. In May of that year, the court denied his appeal against extradition. Hide Caption 9 of 22 Photos: WikiLeaks founder Julian Assange Assange addresses the media and his supporters from the balcony of the Ecuadorian Embassy in London on August 19, 2012. A few days earlier, Ecuador announced that it had granted asylum to Assange. In his public address, Assange demanded that the United States drop its "witch hunt" against WikiLeaks. Hide Caption 10 of 22 Photos: WikiLeaks founder Julian Assange Assange speaks from a window of the Ecuadorian Embassy in December 2012. Hide Caption 11 of 22 Photos: WikiLeaks founder Julian Assange Assange addresses the Oxford Union Society from the Ecuadorian Embassy in January 2013. Hide Caption 12 of 22 Photos: WikiLeaks founder Julian Assange Assange appears with Ecuadorian Foreign Minister Ricardo Patino on the balcony of the embassy in June 2013. Hide Caption 13 of 22 Photos: WikiLeaks founder Julian Assange Assange speaks during a panel discussion at the South By Southwest Festival in Austin, Texas, in March 2014. Hide Caption 14 of 22 Photos: WikiLeaks founder Julian Assange Assange attends a news conference inside the Ecuadorian Embassy in London in August 2014. Hide Caption 15 of 22 Photos: WikiLeaks founder Julian Assange Assange is seen on a video screen in March 2015, during an event on the sideline of a United Nations Human Rights Council session. Hide Caption 16 of 22 Photos: WikiLeaks founder Julian Assange Assange, on the balcony of the Ecuadorian Embassy, holds up a United Nations report in February 2016. The United Nations Working Group on Arbitrary Detention said that Assange was being arbitrarily detained by the governments of Sweden and the United Kingdom. Hide Caption 17 of 22 Photos: WikiLeaks founder Julian Assange Assange speaks to the media in May 2017, after Swedish prosecutors had dropped their investigation of rape allegations against Assange. But Assange acknowledged he was unlikely to walk out of the embassy any time soon. "The UK has said it will arrest me regardless," he said. "The US CIA Director (Mike) Pompeo and the US attorney general have said that I and other WikiLeaks staff have no ... First Amendment rights, that my arrest and the arrest (of) my other staff is a priority. That is not acceptable." Hide Caption 18 of 22 Photos: WikiLeaks founder Julian Assange Assange was seen for the first time in months during a hearing via teleconference in Quito, Ecuador, in October 2018. The hearing was then postponed due to translation difficulties. Hide Caption 19 of 22 Photos: WikiLeaks founder Julian Assange A van displays images of Assange and Chelsea Manning, the former Army intelligence analyst who supplied thousands of classified documents to WikiLeaks, outside the Ecuadorian Embassy in London on Friday, April 5. A senior Ecuadorian official said no decision has been made to expel Assange from the embassy. According to WikiLeaks tweets, sources had told the organization that Assange could be kicked out of the embassy within "hours to days." Hide Caption 20 of 22 Photos: WikiLeaks founder Julian Assange A screen grab from video footage shows the dramatic moment when Assange was hauled out of the Ecuadorian Embassy by police on Thursday, April 11. Assange was arrested for "failing to surrender to the court" over a warrant issued in 2012. Officers made the initial move to detain Arrange after Ecuador withdrew his asylum and invited authorities into the embassy, citing the Australian's bad behavior. Hide Caption 21 of 22 Photos: WikiLeaks founder Julian Assange Assange gestures from a police vehicle on his arrival at Westminster Magistrates' Court in London on April 11. US authorities have also issued an extradition warrant for Assange. The US Department of Justice confirmed Assange has been indicted on conspiracy with Manning. Hide Caption 22 of 22

On Wednesday, Trump championed WikiLeaks founder Julian Assange's claim that Russia wasn't the source of stolen documents from the Democratic National Committee that his group distributed.

McCain asked Clapper whether Assange had endangered men and women serving the US with his earlier release of State Department cables.

"Yes, he has," Clapper said.

McCain then asked whether Assange should be accorded any credibility -- another implicit rebuke of Trump. Clapper responded, "No, he should not."

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The President-elect's apparent support for Assange and his dismissal of the intelligence community's findings on Russia have alarmed fellow Republicans, but on Thursday morning, Trump tweeted that "the media lies to make it look like I am against 'Intelligence' when in fact I am a big fan!"

The intelligence leaders stressed before the Senate that instead of "moving on," Russia requires vigilance.

"Russia is a full-scope cyber actor that poses a major threat to US government, military, diplomatic, commercial, and critical infrastructure and key resource networks because of its highly advanced offensive cyber program and sophisticated tactics, techniques, and procedures," they said.

After Thursday's public hearing, Clapper, Lettre and Rogers may brief lawmakers in a closed session to discuss classified material, Senate aides said. Clapper is due to brief Trump Friday on Russia's actions in a private meeting.

President Barack Obama ordered a full review of Russian meddling into the election a month ago and received the report Thursday morning. Clapper, who will brief Trump on the findings on Friday, said the report will speak to Russia's motivations. He also told lawmakers that an unclassified version will be released to the public.

Speaking to WMAQ in Chicago Thursday, Obama said it was "important" Trump and Intelligence Community work together.

"My hope is that when the President-elect receives his own briefings and is able to examine the intelligence as his team has put together and they see how professional and effective these agencies are, that some of those current tensions will be reduced," Obama said.

"I can speak to my own experience -- it's going to be important to make sure the President and the intelligence communities are both working on the best possible information," Obama continued.

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Showdown with Congress likely

Trump's stance sets up a likely clash with Congress, where the push to probe Russia's actions has been intensifying. Republicans like Graham and McCain want broad investigations into Russian behavior in cyberspace and overseas.

After the hearing, McCain told reporters that Russia's ability to interfere in the elections was "a threat to national security." He added that "In the broadest context, it was an act of war," but said that retaliation would have to be carefully considered.

"It fits the definition of an act of war, but it doesn't mean you start shooting over it," McCain said.

McCain said he didn't know why Trump refuses to accept intelligence conclusions on Russia. Asked if he had any concerns about that, McCain said he wanted to wait until Trump was briefed on Friday.

Graham told CNN in December that he and McCain plan to put sanctions together that hit Russian President Vladimir Putin "as an individual and his inner circle for interfering in our election" and in other nations' elections.

Graham said that there are "a hundred United States senators ... I would say that 99 of us believe the Russians did this and we're going to do something about it."

Meanwhile, a broad array of Democrats are calling for a public airing of Russia's efforts to sway the election. Senior Senate Democrats introduced a bill Wednesday to investigate the election interference.

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Trump's incoming White House press secretary Sean Spicer tried to explain the President-elect's skepticism about the intelligence on Russia in a call with reporters Wednesday, distinguishing between raw data and conclusions drawn from that data.

Trump "is more skeptical of conclusions from raw data, rather than intelligence and raw data provided," Spicer said. "That's why he's looking forward to meeting on Friday."

Intelligence officials describe increasing dismay within their community about Trump's attacks and refusal to believe them.

"It's a sad day when politicians place more stock in Vladimir Putin and Julian Assange than in the Americans who risk their lives daily to provide objective non-partisan intelligence analysis," one official told CNN.

In Thursday's hearing, Connecticut Democratic Senator Richard Blumenthal said Trump's "demeaning and dismissive" comments about intelligence officers were unacceptable and praised their service.

"I want to thank you on behalf of all the women and men in the intelligence community," Clapper said. "I want to thank you for that."