Rep. Adam Schiff (D., Calif.), who was the lead manager in the Senate impeachment trial, watched from the cloakroom as Sen. Mitt Romney delivered his speech announcing that he would vote to convict President Trump of abuse of power.

"It was breathtaking to see someone display that kind of moral courage," Mr. Schiff said.

"This is the past GOP nominee for president who knew the reaction he was going to draw but felt compelled by his faith and the oath that he took to do impartial justice and he lived up to that oath," Mr. Schiff said.

In his closing argument on Monday, Mr. Schiff had pleaded with Republican senators, telling them that even a single vote, by a single member, could change history.

"I mentioned the other day that a single person, a single vote could change history," Mr. Schiff said. "I think he did, and in the future when I face a difficult vote or others face a difficult vote I think we will think back to the courage that he displayed."

Mr. Schiff said that he and colleagues would assess over the next few days whether to continue their investigation, including whether to subpoeana former national security adviser John Bolton to testify. "Nothing's been decided at this point," he said.