Sen. Dick Durbin (D-Ill.) called for an investigation into how the man who shot Rep. Gabrielle Giffords (D-Ariz.) and as many as 19 others in Tucson, Ariz., Saturday obtained a handgun despite a "history of mental instability."
The shooting has launched a fresh debate on gun control laws.
"How did he go through the process and end up with this gun and with this ammunition?" said the Senate majority whip on CNN's "State of the Union." "I think that's a legitimate question."
A suspect, 22-year-old Jared Loughner, is in custody. Media reports indicate that the handgun used in the shooting was obtained legally.
However, freshman Sen. Mike Lee (R-Utah), who appeared later on the program, suggested no amount of laws restricting gun ownership could prevent a person "bent on performing evil acts to kill another person."
Laws are already on the books that prevent mentally ill people from obtaining guns, he said.
"I don't think we're going to legislate our way out of the risk," the Tea-Party backed senator said. "To the contrary, there is abundant research suggesting that in cities where more people own guns, the crime rate, especially the murder rate, goes down."
On NBC's "Meet the Press," Rep. Trent Franks (R-Ariz.) pointed out that the gun used in the shooting was the same used by many police officers.
"It's not that the gun was evil, it's that it was in the hands of an evil person," he said. "I don't know that we can focus in on that."
Updated at 12:11 pm.