Final answer:
Senator Russ Feingold's opposition to the Patriot Act was based on his concern that it would undermine individual civil liberties due to the law's expansive surveillance powers. The correct answer is option: D. He was concerned that enhanced investigations would undermine individual civil liberties.
Step-by-step explanation:
Senator Russ Feingold's opposition to the Patriot Act was based on concerns about civil liberties. Specifically, Feingold was concerned that enhanced investigations enabled by the Patriot Act would undermine individual civil liberties. The Patriot Act expanded the powers of the federal government, allowing for covert surveillance without warrants.
Critics like Feingold worried that this broadened surveillance power could lead to an unwarranted intrusion against the right to privacy and ultimately be used to prosecute ordinary citizens, like in scenarios where drug dealers were targeted more than terrorists. There was also apprehension that such laws might pave the way for further restrictions on citizen rights, signaling a diminishing regard for the freedoms that the United States highly values.