Attorney General Jeff Sessions acknowledges that he discussed then-FBI Director James Comey with President Donald Trump before writing the letter that was used as justification for Comey’s firing in May. But he won’t say what, specifically, Trump’s concerns with Comey were — and in particular, whether Trump was intent on getting rid of Comey to dispel the “cloud” he felt the FBI’s investigation into Russian interference in the 2016 election had cast over his presidency.

In a hearing before the Senate Judiciary Committee, Sessions confirmed to Sen. Dianne Feinstein (D-CA) that he and Deputy Attorney General Rod Rosenstein had met with the president before writing their May 9 letters, which justified firing Comey based on his treatment of the 2016 investigation into Hillary Clinton’s use of a private email server as secretary of state.

But asked whether Trump had ever voiced concerns about a “cloud” over the Russia investigation to Sessions — or what, in particular, Trump’s concerns about Comey were — Sessions claimed the content of his conversations with the president was confidential.

Sessions made it clear in his opening statement to the committee that he’d be less than forthcoming on questions like this: “Under these circumstances today, I will not be able to discuss the content of my conversations with the president.” His argument (which he also made during his previous Senate testimony, before the Intelligence Committee) is that Trump has the right to invoke executive privilege to keep the contents of his interactions with officials private — and that unless the White House explicitly decides not to invoke executive privilege, Sessions can’t deprive them of the option to do so by talking about any conversations that executive privilege might protect.

Many legal scholars think this is a dubious use of executive privilege. But it’s the line that Sessions has drawn when it comes to his interactions with the president, and Senate Democrats haven’t been able to get him to budge.

Nor, for that matter, has special counsel Robert Mueller. Sessions wouldn’t answer a question from Sen. Patrick Leahy (D-VT) about whether he’d gotten any inquiries from Mueller or his team, but would confirm that he hasn’t yet sat down with them for an interview. The implication (as pointed out by former Obama DOJ aide Matthew Miller on Twitter) is that Mueller’s investigators have asked Sessions for an interview, but he hasn’t agreed to it yet.

Ultimately, without Sessions or Rosenstein being willing to talk about what Trump said to them about Comey before they wrote their letters, the public will never know exactly why Trump fired Comey. It’ll be up to everyone to determine what they think is more credible: Sessions and Rosenstein’s claims that a proper process was followed, or Trump’s own stream-of-consciousness associations between Comey and the Russia investigation.

Read the full exchange between Feinstein and Sessions below: