The Washington Post and The New York Times reported Friday that a secret CIA presentation shown to lawmakers revealed that the Russian government interfered with the election to try to help President-elect Donald Trump win.
According to the Post, intelligence officials identified people with connections to the Russian government who they say handed thousands of hacked emails and other documents to WikiLeaks.
"Reports of the CIA's conclusion that Russia actively sought to help elect Donald Trump are simultaneously stunning and not surprising, given Russia's disdain for democracy and admiration for autocracy," Schumer said in a statement Saturday.
Before the election, WikiLeaks regularly published hacked documents that were damaging to Democratic Party organizations and its presidential nominee, Hillary Clinton. The email dump reached a fever pitch in the final weeks of campaigning.
"That any country could be meddling in our elections should shake both political parties to their core," Schumer said. "Senate Democrats will join with our Republican colleagues next year to demand a congressional investigation and hearings to get to the bottom of this."
Schumer said it is "imperative" for the intelligence community to hand over any information that Congress would find useful to its investigation.
The CIA told senators in private meetings last week that their evidence demonstrated it was "quite clear" Russia aimed to help Trump win.
Late Friday night, Trump's transition team disparaged the CIA in responding to the reports.
"These are the same people that said Saddam Hussein had weapons of mass destruction," it said in a statement. "The election ended a long time ago in one of the biggest Electoral College victories in history."
Trump has not personally responded, although he has spoken out on other news since this surfaced. Early Saturday, he dismissed as "fake news" a report by CNN and others that he would retain an executive-producer role on "Celebrity Apprentice."
Sean Spicer, a communications director for the Republican National Committee, stressed Saturday there was no proof that any Russian involvement affected the outcome of the election.
"Donald Trump doesn't think - no one thinks that a foreign entity should be interfering with the US election," Spicer told CNN's Michael Smerconish in a tense interview on Saturday.
"What proof does anyone have that they affected the outcome? Because I've heard zero. Show me what facts that actually show that anything undermined that election," he added.
President Barack Obama ordered a complete review of the matter Friday.