When Durbin took the floor on Tuesday to speak out against the Tester amendment, Tester was serving as the acting pro tempore and unable to respond.

“There is a prohibition in the U.S. Constitution from cruel and unusual punishment, and the fact that you would be presiding in the chair when I am going to be speaking on an amendment which you are offering is truly cruel and unusual, and I'm going to inflict it anyway,” Durbin joked. “I will try to be as gentle as I can in the process.”

The role of pro tempore is considered mundane and ceremonial and is usually performed by junior members of the majority party. Tester is in his first senatorial term. While filling the role, senators are prohibited from participating in debate.

When, later in the morning, Tester spoke from the floor in favor of his amendment, he indicated he was not offended by Durbin’s inauspicious timing.

“I appreciate Senator Durbin's passion on this issue,” Tester said. “I look forward to working with him on the many issues we have in common very soon.”

 Debate over the swipe fee legislation, which could see a vote later this week, is expected to continue throughout the day.