In response to The New York Times exposé, President Trump launched a tweetstorm Sunday, in which he lashed out at both The New York Times and special counsel Robert Mueller’s investigation. In one of the tweets, he wrote, “The Failing and Crooked (but not as Crooked as Hillary Clinton) @nytimes has done a long & boring story indicating that the World’s most expensive Witch Hunt has found nothing on Russia & me so now they are looking at the rest of the World!”

President Trump went on to call for an investigation into his claims his campaign had been surveilled, writing, “I hereby demand, and will do so officially tomorrow, that the Department of Justice look into whether or not the FBI/DOJ infiltrated or surveilled the Trump Campaign for Political Purposes–and if any such demands or requests were made by people within the Obama Administration!”

Trump has been claiming for months, without evidence, that the Obama administration spied on his campaign. Legal experts say his tweet Sunday crossed a line by applying overt presidential pressure on the Justice Department, which could possibly set up a clash similar to the one between President Nixon and the Justice Department during the Watergate scandal. Deputy Attorney General Rod Rosenstein has responded to Trump’s tweet by asking the Justice Department’s inspector general to probe whether the FBI surveilled Trump’s campaign.