Democrats launch sweeping probe targeting dozens in Trump orbit

US Democratic lawmakers on Monday launched their most ambitious investigation yet into alleged obstruction of justice and abuse of office by Donald Trump, targeting dozens of individuals in the president's inner circle.

With controversies swirling around Trump, the powerful House Judiciary Committee's chairman sent strongly worded letters to family members of the president -- including sons Don Jr and Eric -- as well as political confidantes and related entities.

The letters demanded documents that could shed light on possible wrongdoing by the administration and Trump himself.

Son-in-law Jared Kushner and the Trump Organization's long-time chief financial officer, Allen Weisselberg, were among the 81 people and organisations, such as the National Rifle Association, that received letters from the panel's Democratic chairman Jerry Nadler.

They also include White House ex-aides Steve Bannon and Hope Hicks, current Trump personal lawyer Jay Sekulow, former attorney general Jeff Sessions and WikiLeaks founder Julian Assange.

The request is the most serious overt ramp-up of investigations into Trump since Democrats took control of the House of Representatives in early January, and seeks to uncover whether Trump or his administration has participated in obstruction of justice or public corruption -- potentially impeachable offences.

"This is a critical time for our nation and we have a responsibility to investigate these matters and hold hearings for the public to have all the facts," Nadler said in a statement.

"Over the last several years, President Trump has evaded accountability for his near-daily attacks on our basic legal, ethical and constitutional rules and norms," he added.

"Investigating these threats to the rule of law is an obligation of Congress."