Former FBI director James Comey will testify before the Senate Intelligence Committee about whether President Donald Trump pressured him to halt a probe into former national security adviser Michael Flynn's links to Russia.

"I wish him luck," US President Donald Trump (R) said, when asked in a meeting with Republican leaders whether he had a message for former FBI director Comey (L).
"I wish him luck," US President Donald Trump (R) said, when asked in a meeting with Republican leaders whether he had a message for former FBI director Comey (L). (TRT World and Agencies)

The US capital will grind to a halt on Thursday, eyes will be glued to computer and television screens as sacked FBI chief James Comey testifies in Washington about whether President Donald Trump pressured him to halt a probe into an adviser's links to Russia.

Comey's highly anticipated appearance before the Senate Intelligence Committee could be a turning point in a controversy that has rocked Trump's young administration.

Comey is the star witness in the investigation of alleged Russian election meddling last year, with the possible collusion of the Trump campaign. The allegations have drawn comparisons to the 1970s Watergate scandal that brought down then-president Richard Nixon.

The former FBI director was given the go-ahead to deliver potentially explosive testimony after the White House announced it would not use its executive privilege to block his appearance, less than a month after he was controversially sacked by the president.

Comey is expected to dispute Trump's claim that Comey told him multiple times that he was not under investigation by the FBI, CNN reported sources familiar with Comey's thinking as saying.

Trump himself weighed in on Tuesday, even as the revelations could spell more bad news for his troubled administration.

"I wish him luck," Trump said, when asked in a meeting with Republican leaders whether he had a message for the former FBI chief.

With Capitol Hill abuzz, at least two Washington bars were set to open their doors before the hearing's 10:00 am (1400 GMT) start for Washingtonians wanting to tune in live.

"I just hope he tells everything he can," the Senate's top Democrat, Chuck Schumer said.

"The American people, on a subject as serious as this, are entitled to the whole truth and nothing but."

A warm-up act of sorts came Wednesday, when the same committee heard from Director of National Intelligence Dan Coats, National Security Agency (NSA) head Mike Rogers, interim FBI Director Andrew McCabe, and Deputy US Attorney General Rod Rosenstein.

Adding to the drama, a top-secret NSA report leaked to online news outlet The Intercept shows that hackers from Russian military intelligence repeatedly tried to break into US voting systems before last year's presidential election.

Keen to crack down on leaks, the Trump administration quickly announced the arrest of a 25-year-old intelligence contractor on charges of violating the Espionage Act.

"Don't leave me alone with Trump"

Comey's testimony will be his first public remarks since Trump summarily fired him on May 9.

The dismissal – a stunning move by any measure – came as the FBI is probing possible collusion between his campaign team and Russia, which US intelligence agencies concluded sought to tilt the election in the Republican's favour.

Comey is said to have written detailed notes about three conversations he had with Trump, which reportedly document the president's efforts to get the FBI to ease the investigation's focus on former national security adviser Michael Flynn.

The New York Times reported on Wednesday that Comey approached Attorney General Jeff Sessions and said that that he did not want to be left alone with Trump again, after Trump asked Comey to end his investigation into Flynn in February.

Comey did not give a reason as to why he didn't want to be left alone with the president.

Sessions reportedly said that he could not guarantee that Trump would not try to talk to Comey again.

Any confirmation that Trump tried to press Comey would open the president to damaging allegations that he attempted to obstruct an ongoing FBI investigation – which several Democrats have warned would propel the crisis into Watergate-like territory.

Trump himself invoked Nixonian symbolism last month, when he warned via Twitter that Comey "better hope that there are no 'tapes' of our conversations."

Revelations that Nixon secretly taped visits in the White House and refused to turn over the audio tapes under subpoena led to his resignation in 1974.

Senator Mark Warner, the intelligence panel's top Democrat, said Trump would have violated long-standing guidelines if he pressured Comey to drop or slow-walk an investigation.

"It would be unthinkable if the president actually did what was reported," Warner told CBS News Sunday.

"We have no smoking gun at this point, but there is a lot of smoke."

Cautious Comey expected

What Comey will reveal, if anything, is the topic of intense speculation.

Republican committee member Senator Roy Blunt said he welcomed Comey's testimony, but warned there could be "a big problem" if the ousted FBI boss is too restrictive in his responses.

"I expect us to ask him questions to be sure that we get all of the answers we need, not just the answers he wants to give," he said.

However, legal sources expect Comey will likely hold back from accusing Trump of trying to interfere with the FBI investigation.

Two legal experts said Comey would seek to avoid compromising a new enquiry led by Special Counsel Robert Mueller or separate congressional investigations.

"I would expect him to hew pretty closely to facts and events," said Jack Sharman, a partner at Lightfoot, Franklin and White and former special counsel to a congressional committee that investigated former president Bill Clinton in the 1990s.

Another source, who asked not to be named, said Comey does not see it as his role to charge the president or anyone else with obstruction of justice or any other crime.

Trump's decision to fire Comey led the Department of Justice to appoint a special counsel, ex-FBI director Robert Mueller, to investigate allegations of collusion.

He reportedly has met with Comey to discuss the probe, and Comey reportedly sought his approval to testify.

Source: TRTWorld and agencies