WASHINGTON — Days before a highly anticipated hearing, President Trump appears unlikely to try to block fired FBI Director James Comey from testifying, as a Senate panel pledged aggressive questioning into whether the president sought to obstruct a probe into his campaign’s relationship with Russia.

Comey, ousted last month amid the FBI investigation into possible Trump campaign ties to Russia, is due to testify Thursday before the Senate intelligence committee. The public hearing is expected to shed light on his private conversations with Trump in the weeks before his dismissal, including one discussion in which Trump allegedly asked Comey to drop an investigation of former national security adviser Michael Flynn and his Russian contacts.

There’s been no final decision as to whether Trump would invoke executive privilege, and the matter remains under discussion, according to two administration officials. Trump is known to change his mind on major issues.

“Clearly, it would be very, very troubling if the president of the United States is interfering in investigations that affect potentially the president and his closest associates,” said Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee. He said invoking executive privilege would be on “shaky legal ground” and stressed that Comey deserved to have his “day in court” after repeated attacks by Trump and reports of undue pressure.

While acknowledging no “smoking gun at this point,” Warner said he wants “to know what kind of pressure, appropriate, inappropriate, how many conversations he had with the president about this topic.”

The Senate committee also has invited top spy and law enforcement officials to testify Wednesday at a hearing about the federal law governing foreign intelligence collection. Warner said he intended to use that time to ask Director of National Intelligence Dan Coats and National Security Agency Director Adm. Mike Rogers about reports that Trump had urged them to say publicly there was no collusion between the Russians and the Trump campaign.

Acting FBI Director Andrew McCabe and deputy Attorney General Rod Rosenstein also are expected to testify.

“I want to ask those individuals directly, ‘Did they have that kind of pressure?”‘ Warner said, referring to Coats and Rogers.

For Thursday’s hearing, Trump could invoke executive privilege by arguing that discussions with Comey pertained to national security and that he had an expectation of privacy in getting candid advice from top aides. But legal experts say Trump likely undermined those arguments because he publicly discussed the conversations in tweets and interviews. Trump’s argument in favor of privilege also may be overcome because the investigation is focused on corruption and possible obstruction of justice.

In his May 9 letter firing Comey, Trump said the former FBI director had informed him “on three separate occasions that I am not under investigation.” Trump later tweeted: “James Comey better hope that there are no ‘tapes’ of our conversations before he starts leaking to the press!”

Trump also said in an interview that he was thinking of “this Russia thing” when he decided to fire Comey.

Republican Sen. Susan Collins of Maine, also a member of the committee, said she had several questions for Comey in light of various public statements about the ongoing FBI probe, including Trump’s claim that the FBI director had said that Trump was not the subject of an investigation.

“Does Mr. Comey agree that that is what was said? Why would he tell the president that?” Collins asked.

She also cited McCabe’s testimony to the Senate panel last month that “there has been no effort to impede our investigation to date,” which appears to conflict with subsequent news accounts of Comey’s memo detailing a conversation in which Trump allegedly asked him to back off the Flynn probe.

The intelligence committee has asked to review that memo and any other notes Comey put together on his private meetings with Trump, although Warner said that would likely have to be cleared by Robert Mueller, another former FBI director now overseeing the bureau’s investigation as special counsel.

“The tone, the exact words that were spoken and the context are so important,” Collins said. “And we can only get that by talking to those directly involved.”

Warner spoke on CNN’s “State of the Union” and CBS’ “Face the Nation,” Collins also spoke on CBS and Blunt appeared on “Fox News Sunday.”