NASHVILLE, Tenn. (AP) — Former national security adviser John Bolton on Wednesday denounced the House’s impeachment proceedings against President Donald Trump as ”grossly partisan” and said his testimony would not have changed Trump’s acquittal in the Senate, as he continued to stay quiet on the details of a yet-to-be-released book.

In his second public discussion this week, Bolton was on stage at Vanderbilt University with former national security adviser under President Barack Obama, Susan Rice, who questioned Bolton’s refusal to discuss more details while his book undergoes screening for possible classified national security details by the Trump administration. Bolton was likewise quiet on specifics from the book during a Monday speaking engagement at Duke University.

Bolton plans to publish the book next month detailing his time in the White House, including criticism of Trump actions such as his decision to withhold military assistance while seeking a political favor from Ukraine. He said he believes the book doesn’t contain classified information.

Bolton contended that the House “committed impeachment malpractice,” drawing some grumbling from the audience, saying “the process drove Republicans who might have voted for impeachment away because it was so partisan.” He also said he didn’t expect the Senate to vote against having him testify.

“People can argue about what I should have said and what I should have done,” Bolton said. “I would bet you a dollar right here and now, my testimony would have made no difference to the ultimate outcome.”

In leaked passages from the book’s manuscript, Bolton says Trump told him he was conditioning the release of military aid to Ukraine on whether its government would help investigate former Vice President Joe Biden and his son.

Rice said she also underwent a White House pre-clearance process for her own book. She said nothing caused her “to refuse to share information with Congress or the public that I thought was of national import.”

“I can’t imagine withholding my testimony, with or without a subpoena,” Rice said. “I also can’t imagine, frankly, in the absence of being able to provide that information directly to Congress, not having exercised my First Amendment right to speak publicly at a time when my testimony or my experience would be relevant.”

For anyone saying he should just “spill his guts” on what he knows, Bolton cited the “implied threat of criminal prosecution” if what he shares is determined to be classified information. Asked if he would have testified under a House subpoena, Bolton again cited the review process.

“I’m not here to speculate on that with the pre-publication review process under way,” Bolton said, drawing some laughs from the audience. “Laugh all you want. This is the judgment of my counsel, somebody I worked with 35 years ago, 30 years ago at the Department of Justice.”

House Speaker Nancy Pelosi and House Intelligence Committee Chairman Adam Schiff have put off — but not ruled out — a subpoena for Bolton, who refused to participate in the House impeachment inquiry but later said he would testify in the Senate trial.