The senators will likely hone in on discussions between Comey and President Donald Trump about the Russia investigation, and whether the president improperly sought Comey’s loyalty.
But Trump could try to block Comey from testifying about their conversations by asserting executive privilege, which is “the right of a president to withhold information from those with compulsory power -- including special counsels and congressional committees -- but only when it’s in the public interest to do so,” explained Mark Rozell, dean of the Schar School of Policy and Government at George Mason University and author of "Executive Privilege: Presidential Power, Secrecy and Accountability."
Rozell said that Trump can claim the privilege, but it would likely be a losing argument. “The president would have to make the case that if Comey divulges information, it would cause undo public harm by compromising national security or an ongoing investigation,” said Rozell.
Mitch Sollenberger, a political science professor at University of Michigan-Dearborn, agreed, pointing out that courts would balance the public’s interests with the president’s need for secrecy. “If Congress is investigating a potential interference with our elections and if the president had anything to do with it, then Congress and the public need to know,” said Sollenberger.
Legal experts said that Trump’s own comments about his conversations with Comey significantly weaken any case for executive privilege. For example, in a May 9 letter telling Comey that he was fired, Trump wrote: “... I greatly appreciate you informing me, on three separate occasions, that I am not under investigation...”
And on May 12, Trump tweeted: “James Comey better hope that there are no "tapes" of our conversations before he starts leaking to the press!”
“I don’t think it’s appropriate for Trump to claim executive privilege after he’s been writing and tweeting about his conversations with Comey. That makes it very hard for him to now claim the right to secrecy,” said Rozell.
Had Trump kept silent, “He would have had a stronger basis because of the ongoing Russia investigation,” Rozell added.
Executive privilege is a murky legal concept, say experts. It is an “implied power” of the president under Article 2 of the Constitution, but it is not mentioned in the Constitution and there is no statutory definition.
While presidents have the discretion to claim the privilege, “Congressional committees can fight back with their own constitutional tools, including subpoenas, contempt citations, refusals to hold hearings on presidential programs or appointments, or the ultimate tool of impeachment,” said Rozell.
Presidents also face the court of public opinion. Blocking testimony could be politically explosive, experts say, and possibly create the impression that the president has something to hide.
The White House is offering no comment on whether it will claim executive privilege ahead of Comey's scheduled testimony.