This editorial has been updated.

An impeachment trial with testimony from key witnesses is the only fair way for the Senate to render a verdict on whether to remove President Trump from office.

The president himself has demanded no less.

“I would love to have Mike Pompeo. I’d love to have Mick. I’d love to have Rick Perry and many other people testify. But I don’t want them to testify when this is a total fix,” Mr. Trump said last month when asked why so many of his top administration officials — including his secretary of state; his acting chief of staff, Mick Mulvaney; and his former energy secretary — were not testifying in impeachment hearings in the House of Representatives. “I want them to testify in the Senate where they’ll get a fair trial.”

Mr. Trump omitted one pertinent name from that list: John Bolton, his former national security adviser. Mr. Bolton may know as much as anyone in the administration about what Mr. Trump was doing when he froze hundreds of millions of dollars in military aid to Ukraine.

On Monday, Mr. Bolton announced that he would be willing to testify in a Senate trial if subpoenaed. He had previously declined to appear before the House, saying he would wait for a federal court to rule first on a constitutional dispute between Congress and the White House, which had ordered him and others not to testify.