Fellow Republicans on Sunday pressed US President Donald Trump to come clean about whether he has tapes of private conversations with former FBI director James Comey.
They also urge Trump to provide the tapes to Congress if he does or possibly face a subpoena as a Senate investigation into collusion with Russia – and possibly obstruction of justice – extended to a Trump cabinet member.
It was a sign of escalating fallout from Comey's riveting testimony last week detailing undue pressure from Trump, which drew an angry response from the president on Friday that Comey was lying.
"I don't understand why the president just doesn't clear this matter up once and for all," said Senator Susan Collins, a Republican from Maine and a member of investigative committee, referring to the existence of any recordings.
She described Comey's testimony as "candid" and "thorough".
Collins said she would support a subpoena if needed, adding Trump "should voluntarily turn them over."
Senator James Lankford, a Republican from Oklahoma, also a member of that committee, agreed the panel needed to hear any tapes that exist. "We've obviously pressed the White House," he said.
But pressed on the issue Friday, Trump said: "I'll tell you about that maybe sometime in the very near future."
Lankford said Sessions' testimony on Tuesday will help flesh out the truth of Comey's allegations, including Sessions' presence at the White House in February when Trump asked to speak to Comey alone.
Comey on the hot seat
Comey alleges that Trump privately asked him to drop a probe into former national security adviser Michael Flynn's contacts with Russia.
Comey said Sessions did not respond when he complained he didn't "want to get time alone with the president again."didn't "want to get time alone with the president again."
The justice department has denied that, saying Sessions stressed to Comey the need to be careful about following appropriate policies.
"We want to be able to get his side of it," Lankford said.
Senator Jack Reed said, "There's a real question of the propriety" of Sessions' involvement in Comey's dismissal because Sessions had stepped aside from the federal investigation into contacts between Russia and the Trump campaign.
Comey was leading that probe when he was fired.
Reed said he also wants to know if Sessions had more meetings with Russian officials as a Trump campaign adviser than have been disclosed.
Trump calls Comey cowardly
Comey's testimony drew invective from Trump on Twitter as he dismissed him as a leaker on Friday and a coward on Sunday.
I believe the James Comey leaks will be far more prevalent than anyone ever thought possible. Totally illegal? Very 'cowardly!'— Donald J. Trump (@realDonaldTrump) June 11, 2017
"I believe the James Comey leaks will be far more prevalent than anyone ever thought possible. Totally illegal? Very 'cowardly!'" Trump tweeted on Sunday.
The president denied trying to interfere with the investigation and said he would be willing to testify under oath about his interactions with Comey.
Several Republican lawmakers also criticised Comey for disclosing memos he had written in the aftermath of his private conversations with Trump, calling it as "inappropriate."
But, added Lankford "releasing his memos is not damaging to national security."
"Unusual" phone calls
Former US Attorney Preet Bharara revealed on Sunday that he received a handful of "unusual" phone calls from Trump after the November election, making him feel uncomfortable.
Bharara said he was fired after declining to take the third call.
Bharara told ABC's show This Week that Trump was trying to "cultivate some kind of relationship" with him when he called him twice before the inauguration to "shoot the breeze".
He said Trump reached out to him again after the inauguration but he refused to call back, shortly before he was fired.
On Comey's accusations that Trump pressed him to drop the FBI investigation of Flynn, Bharara said, "No one knows right now whether there is a provable case of obstruction" of justice.
But, "I think there's absolutely evidence to begin a case."
Democratic Senator Dianne Feinstein of California, a member of the Intelligence Committee, sent a letter to Senator Chuck Grassley, urging him to investigate possible obstruction of justice by Trump. Grassley is the chairman of the Senate Judiciary Committee.
She said Sessions should also testify before the judiciary committee because it was better suited to explore legal questions of possible obstruction.
Feinstein said she was especially concerned after National Intelligence Director Dan Coats and National Security Agency Director Michael Rogers refused to answer questions from the intelligence committee about possible undue influence by Trump.
Feinstein said she did not necessarily believe Trump was unfit for office, as House Democratic leader Nancy Pelosi has asserted.
But Feinstein said he has a "destabilising effect" on government.
"There's an unpredictability. He projects an instability," Feinstein said.
"Doing policy by tweets is really a shakeup for us because there's no justification presented."