Until now, neither the White House nor the Pentagon had publicly confirmed the operation, which had been classified.
Trump sought to frame his action as an example of being more aggressive than his predecessor in countering the Kremlin. President Barack Obama, he said, “knew before the  election that Russia was playing around. Or he was told. Whether or not it was so or not, who knows? And he said nothing.”
In fact, the Obama administration publicly called out Moscow in October 2016 for its hacking of Democratic computers, and Obama directly raised the matter with Russian President Vladimir Putin. In December of that year, Obama imposed sanctions on Russia over its interference in the presidential election.
Still, the admission is a rare instance of Trump acknowledging that Russia had malign intent with respect to American democracy. He even seemed to brag about his role in deterring such efforts.
“Look, we stopped it,” the president told Thiessen.
The admission comes as U.S. intelligence officials have warned that Russia will seek to disrupt this year’s presidential election.
For the most part, Trump has avoided acknowledging such warnings and that Russia has sought to sow discord in the United States, even siding with Putin in his denials that Moscow interfered in the 2016 presidential elections — despite his intelligence agencies’ conclusion to the contrary.
The Washington Post last year reported on the U.S. Cyber Command operation against the Internet Research Agency in St. Petersburg, a company underwritten by an oligarch close to Putin. The agency’s trolls were active during the 2016 campaign, posing as Americans to post material online in an effort to stoke conflict by exploiting racial and other societal tensions.
The operation was part of the first offensive cyber-campaign against Russia designed to thwart attempts to interfere with a U.S. election, officials told The Post. It marked the first use by Cybercom of new authorities granted by Trump and Congress in 2018 to bolster offensive capabilities.
The attack began on Election Day and lasted several days, preventing the Russians from mounting a disinformation campaign that cast doubt on the election results, officials said.
The Russian Embassy did not respond to a request for comment.