Among the people listed in the request for documents include some of Trump's closest associates and family members, including his two sons - Eric Trump and Donald Trump Jr., son-in-law Jared Kushner, his campaign manager Brad Parscale, former aides Hope Hicks and Don McGahn and longtime employees of the Trump Organization like chief financial officer Allen Weisselberg, and Rhona Graff, a longtime gatekeeper to Trump.
Burnett asks Nadler: Why isn't Ivanka Trump on your list?
The investigation was subsequently taken over by Special Counsel Robert Mueller, who is expected to end his investigation and report his findings in coming weeks.
House Democrats say they have been careful to avoid conflicts with Mueller's investigation into Russian interference in the 2016 U.S. election and possible coordination with the Trump campaign, as well as federal probes being led by the U.S. Attorney's Office in Manhattan.
In a letter to the White House and State Department, the House intelligence, Foreign Affairs and Oversight and Reform panels sent broad requests for details about Trump and Putin's private meetings by phone and in person.
And a year ago, the White House announced that it would stop the practice of regularly issuing readouts of phone calls between Trump and foreign leaders, which means the public has no idea how often he speaks with Putin by phone.
"We don't have the facts yet", Nadler said.
Separate congressional probes are already swirling around the president, including an effort announced Monday by three other House Democratic chairmen to obtain information about private conversations between him and Russian President Vladimir Putin. Asked about the Nadler investigation on Monday, Trump replied, "I cooperate all the time with everybody.You know the attractive thing - no collusion".More news: The Sunday Edition: President Donald Trump Tweetstorm
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Democrats secured the majority in the House of Representatives in the 2018 midterm election, and with it, the power to launch investigations.
"These allegations, if true, raise profound national security, counterintelligence and foreign policy concerns, especially in light of Russia's ongoing active measures campaign to improperly influence American elections", they wrote.
In a request sent to the White House, the committee asks for information surrounding former FBI Director James Comey's termination, communications with Justice Department officials, the Trump Tower meeting and multiple other matters.
White House press secretary Sarah Sanders said the White House had received the letter and "the counsel's office and relevant White House officials will review it and respond at the appropriate time".
Nadler said Monday the investigation will be focused on possible obstruction of justice, corruption and abuse of power.
"We're far from making decisions" about impeachment, he said.
Warner said he will reach his decision on whether Trump colluded with Russian Federation to help him win the election after more investigation.
House Minority Leader Kevin McCarthy, R-Calif., on Sunday accused House Democrats of prejudging Trump as part of a query based on partisan politics. They said they intend to probe "the substance of any communications during in-person encounters and phone calls, the existence and contents of any documents related to the communications, what the effects of the communications have been on the nation's foreign policy, whether the president or anyone acting on his behalf have sought to hide those communications and whether the president or anyone acting on his behalf have failed to create records or mishandled those records in violation of federal law".