A small but growing number of Republican US lawmakers have called for an independent probe of possible collusion between President Donald Trump's 2016 campaign and Russia, spurred by a memo from the fired FBI chief that Trump had sought to impede the agency's investigation.
The tumult in Washington deepened on Tuesday over allegations Trump had sought to end the FBI's investigation into ties between Trump's first national security adviser, Michael Flynn, and Russia.
James Comey, whose firing as FBI director last week triggered a political firestorm, wrote a memo detailing Trump's comments to him in February saying 'I hope you can let this go,' referring to the Flynn probe, according to a source who has seen a memo written by Comey.
US stocks opened sharply lower on Wednesday after the reports of the memo.
Democratic lawmakers have demanded that the Justice Department name a special prosecutor to investigate potential ties between Trump's campaign and Russia.
But most Republicans have said the current Federal Bureau of Investigation probe and investigations in the Republican-led Congress are sufficient.
House of Representatives Speaker Paul Ryan stuck to that line and told reporters on Wednesday he still has confidence in Trump. Ryan also insisted the Trump controversies were not paralysing Republican legislative efforts in Congress.