What did Donald Trump do today?

He said he'd try to block John Bolton from testifying in his impeachment trial.

It has been less than a month since Trump was impeached for abusing power by trying to force the government of Ukraine to help him in the 2020 election, and for obstruction of Congress by trying to cover it up. For much of that time, Trump has at least pretended to welcome the trial in the Senate, and—contrary to his own party's efforts to protect him—has said he wanted witnesses called. 

In this, at least, history would be on Trump's side. Every one of the fifteen other impeachment trials ever conducted, whether of a president or lesser officials, has involved testimony from witnesses.

But in an interview airing tonight with Laura Ingraham of Fox News, Trump flip-flopped on whether witnesses were a good thing—at least when the witness might actually be able to incriminate him. Trump said he would try to prevent John Bolton, his former national security advisor who objected to the "drug deal," as he called it, of Trump's political appointees trying to force Ukraine to declare a phony investigation of Joe Biden's son in order to influence the election.

Bolton, a conservative Republican, said earlier this week he would obey a subpoena to testify in the Senate trial. It's not clear whether Trump can muster up enough Republican votes in the Senate to write the rules in a way that would allow him to escape having witnesses called at his trial.

Why should I care about this?

• In the history of trials, no one has ever tried to block the testimony of a witness who could exonerate them.