A US House panel investigating alleged obstruction of justice and abuse of power by the White House has sought documents from 81 people and groups.
While extremely broad, Nadler's inquiry focuses on abuse of power, public corruption and obstruction of justice since Trump became president, though some of the inquiries also deal with the campaign and the presidential transition.
Since taking power in the wake of November's midterm elections, House Democrats have vowed to investigate Trump's presidency and business as they await the special counsel Robert Mueller investigation's findings.
As evidence of obstruction, Nadler cited Trump's firing of former FBI Director James Comey, who at the time was leading an investigation into Russia's alleged interference in the 2016 USA presidential election and possible collusion between Trump's campaign and Moscow.
"Congress has a constitutional duty to conduct oversight over the Department and the White House to determine, among other things, the impact of those communications [between Trump and Putin] on USA foreign policy, whether federal officials, including President Trump, have acted in the national interest, and whether the applicable laws, regulations, and agency procedures with respect to diplomatic communications with President Putin and other foreign leaders have been complied with and remain sufficient", Chairmen Adam Schiff (D-CA), Elijah Cummings (D-MD) and Eliot Engel (D-NY) wrote.
Nadler's requests come as House Democrats are ramping up numerous investigations of the president, their first steps in a months-long effort that could lead to impeachment proceedings.
Democrats say Cohen's testimony before the House Oversight Committee last week directly implicated Trump in various crimes including campaign finance violations.
The announcement of the new investigation follows a bad political week for the president.
Various current and former Trump administration officials have been hit with document requests, including Steve Bannon, Sean Spicer, Michael Flynn, Paul Manafort, Roger Stone, Donald Trump Jr., Eric Trump and Jared Kushner, among others.
The House Judiciary Committee sent letters to 81 people and entities linked to Trump, demanding documents within two weeks about a lengthy list of events involving the country's 45th president. Our country is in crisis, and we need someone who knows how to bring people together and get things done.
The House Oversight and Reform Committee received testimony from Cohen last Wednesday in a high-profile hearing where the president's former lawyer accused Trump of lying to the public about his business interests in Russian Federation, his role in silencing women who alleged sexual encounters during the 2016 election and his knowledge of WikiLeaks's hacked material damaging Clinton.
On Saturday, he launched a furious attack on Special Counsel Robert Mueller, railing against the inquiry he was leading into alleged collusion between his campaign and Russian Federation.
"Show me where the president did anything to be impeached.Nadler is setting the framework now that the Democrats are not to believe the Mueller report", he said. The panel will also look into corruption claims. He tried to-he fired-he tried to protect Flynn from being investigated by the Federal Bureau of Investigation.
"It's very clear that the Ppresident obstructed justice", Mr Nadler said.