Many of the individuals who received a letter from Nadler—including Trump’s son Donald Trump Jr.; his son-in-law, Jared Kushner; and the former top White House aides Hope Hicks, Sean Spicer, and Steve Bannon—have already testified before Congress and provided documents in conjunction with the various probes into Trump’s ties to Russia. In the new letters sent out on Monday, which addressed everyone from the Trump Organization’s Chief Financial Officer Allen Weisselberg to the Russian oligarch Viktor Vekselberg, Nadler wrote that the House Judiciary Committee is investigating “a number of actions that threaten our nation’s longstanding commitment to the rule of law, including allegations of obstruction of justice, public corruption, and other abuses of power … President Trump and his administration face wide-ranging allegations of misconduct that strike at the heart of our constitutional order.” He added that “Congress has a constitutional duty to serve as a check and balance against any such excesses,” and that the House Judiciary Committee “has also played a historic role as the primary forum for hearings on the abuse of executive power.”

The document requests varied in subject and scope. In a request to the former Trump campaign adviser Carter Page, for example, Nadler appears to be homing in on alleged collusion between the campaign and Russia. (Trump said on Monday that he cooperates “all the time with everybody … You know the beautiful thing — no collusion. It’s all a hoax.”) Nadler asked for all documents relating to changes to the Republican platform in 2016 dealing with Russia and Ukraine, discussions of sanctions policy with regard to Russia, and the June 2016 Trump Tower meeting between Trump campaign officials and a Russian lawyer. In a letter to the FBI, meanwhile, Nadler seems to be zeroing in on questions of potential obstruction, asking for any communications involving Trump and his associates about the firing of former FBI Director James Comey in May 2017. And in a letter to the CEO of American Media, David Pecker, Nadler requested more information about payments made to the benefit of the Trump campaign that might have violated campaign-finance laws. The Trump campaign’s digital director, Brad Parscale (now Trump’s 2020 campaign manager), received one of the most extensive document requests, covering everything from plans for a Trump Tower Moscow in 2016 to Trump’s conversations with Russian President Vladimir Putin in 2017 and 2018.

Two House Judiciary Committee sources, who spoke on the condition of anonymity to comment freely on the investigation, said some witnesses were asked specific questions “because we’re pretty sure they know” the answer, while other questions were more speculative in nature. But none of the witnesses were hit with completely new document requests that haven’t been asked of them before, by either the special counsel, the Southern District of New York, or various congressional committees. Even more document requests could be sent out to additional witnesses as the investigation moves forward. “This is just the first wave,” one source said. “The committee will continue to make news as the weeks go on.”