A Democratic push to force Republicans to accept witnesses at Donald Trump's impeachment trial in the U.S. Senate appeared to be flagging on Wednesday, raising the possibility the president could be acquitted as early as Friday.

As senators spent the day posing questions to both the Trump legal team and the Democratic managers of the trial, the White House objected to the planned publication of a book by former national security adviser John Bolton, who is said to have depicted Trump as playing a central role in pressuring Ukraine to investigate Democratic rival Joe Biden.

U.S. Sen. John Barrasso, the No. 3 Republican in seniority, said it was possible the trial could end on Friday without Democrats achieving their goal of having witnesses called to testify.