Placing himself at odds once again with American intelligence agencies, US President-elect Donald Trump said Sunday it's "ridiculous" to conclude that Russian-backed hackers sought to boost his chances of winning the White House.

Mr. Trump made the comments to Chris Wallace on "Fox News Sunday" in response to reports that the Central Intelligence Agency (CIA) had concluded, with a high degree of confidence, that the cyber intruders who stole then leaked emails belonging to Democratic leaders had done so to help the Republican nominee. While the Obama administration and a bipartisan group of senators have vowed to investigate the alleged Russian plot further, Trump's own words publicly dismissing the findings could set the stage for drama during his crucial early days in office.

"I see the danger of a lasting dysfunctional relationship based on the president-elect’s perception that he is being wronged by the intelligence community," Paul Pillar, former deputy director of the CIA’s Counterterrorism Center, told The Washington Post, citing Trump's "proclivity for revenge combined with his notorious thin skin."

Trump would not be the first US president to arrive in Washington on Inauguration Day with deep suspicion, even hostility, directed toward intelligence officials. President Richard Nixon, for instance, had a tense relationship with the intelligence community. But Trump's dealings could prove to be even more fraught because of his tendency to be vindictive, Mr. Pillar added.

When he was sworn in, Mr. Nixon knew that American spies had gathered information about his campaign's contact with South Vietnamese government leaders, so he took care to avoid publicly attacking the intelligence community, according to national security historian Timothy Naftali, a New York University professor and former director of the Richard Nixon Presidential Library and Museum.

"I believe he was sensitive to the fact that they had this hanging over his head, and he likely resented it," Dr. Naftali told The Wall Street Journal, adding that there could be a lesson here for the current president-elect.

"It’s a surprise to me that Donald Trump would attack the professionalism of the CIA in light of his possible vulnerability to the release of classified information held by the United States government," Naftali said.

After months of investigation, the Obama administration announced Oct. 7 that "only Russia's senior-most officials could have authorized" the scope of politically motivated hacking perpetrated against the Democratic National Committee and other political organizations. (The announcement stopped short of saying the hackers had sought to favor Trump over Democratic nominee Hillary Clinton.)

Two days later, however, Trump emphatically repeated his assertion that there is insufficient evidence to blame Russia for the recent political hacking.

"Maybe there is no hacking," Trump said Oct. 9 during the second presidential debate. "But they always blame Russia. And the reason they blame Russia because they think they’re trying to tarnish me with Russia."

Trump made similar statements during the first and third presidential debates as well – statements he echoed Sunday when Mr. Wallace asked for his reaction to the CIA's conclusions as conveyed in reports published Friday by The Washington Post.

"I think it’s ridiculous," Trump replied. "I think it’s just another excuse. I don’t believe it. I don’t know why, and I think it’s just – you know, they talked about all sorts of things. Every week it’s another excuse. We had a massive landslide victory, as you know, in the Electoral College. I guess the final numbers are now at 306, and she’s down to a very low number. No, I don’t believe that at all."

Trump went on to claim that attribution in the event of a cyber attack is so difficult that officials cannot know who has hacked them unless they intercept the hack in real time.

"Once they hack, if you don’t catch them in the act, you’re not going to catch them," Trump said. "They have no idea if it’s Russia or China or somebody. It could be somebody sitting in a bed some place. I mean, they have no idea."

An investigation by the White House ordered Friday by President Obama is expected to conclude before he leaves office Jan. 20, but its findings may not be made public, the president’s top counterterrorism adviser said at a breakfast hosted by The Christian Science Monitor.

"We want to [be] very attentive to not disclosing sources and methods that may impede our ability to identify and attribute malicious actors in the future," Lisa Monaco told reporters.

In addition to the executive branch's probe, a bipartisan group of four senators – John McCain (R) of Arizona, Lindsey Graham (R) of South Carolina, Charles Schumer (D) of New York, and Jack Reed (D) of Rhode Island – said Sunday that the legislative branch must investigate as well.

"While protecting classified material, we have an obligation to inform the public about recent cyberattacks that have cut to the heart of our free society," the senators said in a joint statement. "Democrats and Republicans must work together, and across the jurisdictional lines of the Congress, to examine these recent incidents thoroughly and devise comprehensive solutions to deter and defend against further cyberattacks."

"This cannot become a partisan issue," they added. "The stakes are too high for our country."

Trump's statements drew critique from Republicans and Democrats in the House as well.

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"One would also have to be willfully blind not to see that these Russian actions were uniformly damaging to Secretary Clinton and helpful to Donald Trump," Rep. Adam Schiff (D) of California said in a statement. "I do not believe this was coincidental or unintended."

There's no doubt that the Russians hacked our institutions. This was not China or a 400 pound guy in New Jersey. This was the Russians. pic.twitter.com/C6pXWm6B4X — Adam Schiff (@RepAdamSchiff) December 11, 2016

Rep. Devin Nunes (R) of California said Russia has clearly been willing to manipulate elections across the world, but he downplayed the Kremlin's potential role in this year's political hacking.

"Any American can turn on his TV right now and watch Russia’s RT, which is a clear Russian propaganda channel," Mr. Nunes, chairman of the House Intelligence Committee, said, as the Journal reported. "However, there is no evidence that I have seen or witnesses that I have listened to who show the Russians were trying to help Trump."