Senator Martha McSally of Arizona became the second Republican standing for election in a swing state to announce on Wednesday that she would vote against calling new witnesses and documents in President Trump’s impeachment trial.

“I have heard enough,” Ms. McSally wrote on Twitter. “It is time to vote.”

Hours earlier, Senator Cory Gardner, Republican of Colorado, said he had reached a similar conclusion. Their stances were a positive sign for Republican leaders hoping to end the trial this week without compelling new evidence, though several key moderate Republicans remain publicly undecided before the vote expected on Friday.