Sen. Ben Nelson was among members of the Senate Armed Services Committee who questioned Major General Antonio Taguba and others during a committee hearing Tuesday.
Nelson challenged Taguba on the general's statement that a brigadier general bore responsibility for a breakdown in discipline that led to abuse.
Nelson said he thinks the abuse was part of a systematic effort to break down prisoners.
Nelson also responded to a video posted on an Islamic militant Web site that showed the apparent beheading of an American civilian in Iraq. Nelson said U.S. military abuses of Iraqi prisoners will unfortunately be used as an excuse for some to retaliate.