"I think it's just another excuse," he told host Chris Wallace. "I don't believe it. They have no idea if it's Russia or China or somebody. It could be somebody sitting in a bed someplace."
But U.S. Senator and former Republican presidential candidate John McCain wasn't as dismissive. "The facts are there," he said during an interview on Face the Nation Sunday. "Whether [the Russian government] intended to interfere to the degree that they were trying to elect a certain candidate, I think that's a subject of investigation. But facts are stubborn things. They did hack into this campaign."
Here's what we know so far about the alleged hack.
Why would Russia want to hack our election?
Hackers with ties to the Russian government sought and obtained the emails of prominent Democratic Party officials, including Hillary Clinton campaign manager John Podesta. They disclosed information to Wikileaks, yet held off on giving similar information obtained from hacking Republican leaders during the campaign.
This goes beyond what the intelligence committee alleged in October, when the Director of National Intelligence and the Department of Homeland Security put out a joint statement saying that the Russian government "intended to interfere with the U.S. election process" in hacking the emails of several political leaders.
But these hacks, it was believed, were meant to disrupt confidence in the integrity of the election. Now the motivations seem to be more nefarious, with intelligence officials claiming the hacks were meant to influence the election specifically toward helping Trump to win the election.
Joint letter urging bipartisan inquiry
On Sunday, four high-profile U.S. Senators from both political parties issued a joint statement on the recent intelligence findings. Democrats Chuck Schumer and Jack Reed, along with Republicans John McCain and Lindsey Graham, urged further investigation into the matter, saying the interference into the election "should alarm every American."
"This cannot become a partisan issue," the statement said. "The stakes are too high for our country."
The Trump-Russia connection
The CIA's allegations come amid swirling rumors that Trump plans to tap ExxonMobil CEO Rex Tillerson as his secretary of state. Tillerson has some very strong ties to Russia and has even received an Order of Friendship medal from Russian President Vladimir Putin. "It's a matter of concern to me that he has such a close personal relationship with Vladimir Putin," McCain said of Tillerson, raising some doubts about how easy his confirmation in the Senate may be.
Trump's own dealings with Putin got him into some hot water earlier this year. Trump downplayed his connection to the head of state: "I know nothing about Russia," he said during the second presidential debate. But just days after the election, the Russian government said otherwise, suggesting that several members of Trump's campaign team had been keeping in touch with the Kremlin.
Trump also actively encouraged Russian hackers to dig into his opponent's record in July. "Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Trump said, much to the dismay of U.S. security experts.