White House staff have been left reeling from the latest Russia-related controversy as a senior senator even raised the prospect of impeaching Donald Trump.

West Wing staff have spoken of how the chaotic events of the last few days have had a "numbing effect", in particular over reports that the president tried to convince former FBI Director James Comey to shut down a federal investigation into his former national security adviser, Michael Flynn.

One senior official in the Trump administration offered a blunt assessment to the Daily Beast of the continued chaos at the White House, saying: "I don't see how Trump isn't completely f****d."

"I feel like running down the hallway with a fire extinguisher," another senior official told the Daily Beast.

Another staffer said: "We can't even wrap up one Russia fiasco before we're on to the next one."

Senator for Maine, Angus King (I-ME), said that if the claims about a paper trail by Comey suggesting that Trump was trying to affect the investigation were true, it would be a step towards the impeachment process "because obstruction of justice is such a serious offence".

He told CNN: "But, if indeed the president tried to tell the director of the FBI, who worked for him, that he should drop an investigation—whether it was Michael Flynn or some investigation that had nothing to do with Russia or politics or the election—that's a very serious matter."

The senator has called on the White House to provide evidence to refute the New York Times story. The White House has denied the report and said Trump never asked Comey or anyone else to end any investigation, "including any investigation involving General Flynn".

"If the White House has been saying all day that this never happened, then I think they should come forth with whatever evidence that they have, whether it's tapes or notes made by someone at the White House, to contradict this," King said.

Trump suggested on Friday (12 May) that there may have been tapes of conversations he had with Comey. Democratic members of Congress, including Representatives Elijah Cummings (D-Md.) and Filemon Vela (D-Texas), have also discussed the possibility of impeachment, HuffPost reported.

According to The New York Post, House Intelligence Committee member Representative Adam Schiff (D-CA) has called on Comey to testify before Congress about his alleged conversations with the president.

"I think we know enough now, and there has been enough alleged publicly, to want to bring the director back to testify, ideally in open session either before our committee or the Judiciary Committee," Schiff said to reporters.

In an interview with CBS News' Nancy Cordes, Schiff said there is "mounting concern" about how the Trump administration "appears to be interfering with the Russia investigation".

Donald Trump
US President Donald Trump listens to Turkey's President Recep Tayyip Erdogan as they give statements to reporters in the Roosevelt Room of the White House in Washington on 16 May 2017 REUTERS/Kevin Lamarque