U.S. President-elect Joe Biden said on Tuesday that a widespread data breach of the government apparently carried out by the Russian government poses a “grave risk” to national security that cannot “go unanswered.”

At a news conference, Biden faulted President Donald Trump for stripping U.S. defenses against cyber attacks, saying, “This assault happened on Donald Trump’s watch, when he wasn’t watching.” Biden said his administration will take meaningful steps to respond to the breach.