He also feuded with Liberal Republican senators Charles Sumner and Carl Schurz over many issues. He delivered a sarcastic denunciation of Sumner's wide-reaching civil rights amendment to the Confederate amnesty bill. As the chair of an investigating committee he also debunked Sumner and Schurz's claim that the War Department had broken its neutrality when it sold outmoded rifles to France during the Franco-Prussian War. Despite such skirmishes Carpenter was a respected figure in the senate, being elected president pro tempore by his colleagues in 1871. He also served as chairman of the Committee on Enrolled Bills (42nd Congress) and the Committee to Audit and Control the Contingent Expense (42nd and 43rd Congresses).