‘I took an oath,’ Rusty Bowers, Arizona House speaker, says of rejecting efforts to overturn the election.

Mr. Bowers again rejected the push, saying, “I took an oath — for me to take that, to do what you do would be counter to my oath.”

Finally, he testified, there was a call from another Trump supporter, Representative Andy Biggs, Republican of Arizona, on the morning of Jan. 6, 2021, when the Electoral College vote was to be confirmed by a joint session of Congress. Mr. Biggs, he said, pushed him again to undo the state’s certification of its electors for Mr. Biden.

“We have no legal pathway” to “execute such a request,” Mr. Bowers recalled saying. He also recalled his reaction when he learned that Trump advisers pushed ahead with a scheme to put forward slates of “alternate” electors. “I thought of the book, ‘The Gang That Couldn’t Shoot Straight,’” Mr. Bowers said.

Mr. Bowers’s personal journal contained an entry in which he said, “I do not want to be a winner by cheating. I will not play with laws I swore allegiance to.” He was invited to read it into the testimony.

He was also asked for his reaction to a statement from Mr. Trump criticizing Mr. Bowers’s testimony in advance, in which he claimed that Mr. Bowers had told him the election was “rigged” and that he had won the state.

“I did have a conversation with the president,” Mr. Bowers said. “That certainly isn’t it.”

A moment later, more emphatically, he said, “Anywhere, anyone, any time has said that I said the election was rigged — that would not be true.”