WASHINGTON (AP) — Could President Donald Trump keep former FBI Director James Comey from testifying to lawmakers about their private conversations?

The White House appears to be considering raising the issue of executive privilege, but Trump may have a weak case for claiming that his conversations with Comey should be considered private — especially since the president himself has commented publicly about the circumstances surrounding Comey’s May 9 firing.

Comey is set to testify Thursday before the Senate intelligence committee. He’ll likely be asked to recount conversations with Trump about Russian meddling during last year’s election and the FBI’s investigation into former national security adviser Michael Flynn.

“The president will make that decision,” White House adviser Kellyanne Conway told ABC’s “Good Morning America” on Thursday when asked if Trump would try to block Comey’s testimony.

White House press secretary Sean Spicer would not rule it out. He said the committee hearing was just set and “it has to be reviewed.” He said he has not discussed the matter with White House counsel, adding, “I don’t know how they’re going to respond.”

Some questions and answers about executive privilege:

WHAT IS EXECUTIVE PRIVILEGE?

The term “executive privilege” is not in the U.S. Constitution. But it has been invoked by presidents since George Washington to withhold private White House deliberations and records from Congress.

The idea is that presidents should expect to get candid advice from top aides without worrying about revealing it to Congress. The term wasn’t coined until the 1950s, when President Dwight Eisenhower tried to shield administration officials from being questioned in Sen. Joseph McCarthy’s hearings about communism.

The Supreme Court formally recognized the doctrine during the Watergate crisis as part of the balance between the executive branch and Congress. While the justices said conversations between presidents and top aides were presumed confidential, they said the privilege is not absolute. The court ruled that President Richard Nixon’s audio recordings of White House conversations should be turned over to prosecutors.

WHEN WAS IT LAST USED?

President Barack Obama invoked executive privilege in a bid to stop Congress from seeing records about Operation Fast and Furious, a botched gun-smuggling investigation that lost track of about 1,400 guns. Congress voted to hold Attorney General Eric Holder in contempt for failing to turn over the records. A federal judge later rejected Obama’s use of executive privilege and Congress got the documents.

HOW STRONG A CASE COULD TRUMP MAKE TO BLOCK COMEY’S TESTIMONY?

Comey is likely to testify about the FBI’s investigation into possible connections between Russia and the Trump campaign and whether Trump tried to interfere with the probe. Trump could argue that discussions with Comey pertained to national security and had the expectation of privacy.

But Trump likely undermined those arguments because he has already discussed the conversations in tweets and interviews, according to Mitch Sollenberger, a political science professor at the University of Michigan-Dearborn.

In his 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.

“This isn’t something that the president has denied,” Sollenberger said. “That actually weakens his argument against executive privilege.”

Sollenberger said any argument in favor of privilege also could be overcome because the investigation is focused on corruption and possible obstruction of justice.

IF TRUMP TRIES TO USE EXECUTIVE PRIVILEGE, COULD COMEY DEFY HIM?

Comey has indicated that he wants to testify. He is now a private citizen, so he doesn’t have to fear retaliation for defying Trump.

He has an incentive to push back against the White House portrayal of him as unfit for office. Comey’s associates have said Comey told them Trump had asked for a pledge of loyalty to the president and later asked Comey to consider ending the investigation of Flynn. The White House has denied those characterizations.

HOW COULD CONGRESS RESPOND?

If Comey refuses to testify, Congress could subpoena him and then find him in contempt of Congress. The matter would then go to federal court, which could take months to resolve the dispute.