A spokeswoman for Republican Greg Ganske says Ganske’s opponent, Democrat Tom Harkin, has to have others “do his dirty work” because Harkin has a poor record on the prescription drug issue. Yesterday, North Carolina Senator John Edwards criticized Ganske for failing to support a bill that would prevent drug companies from extending patents, a process that keeps cheaper generics off the market. Ann Warren, a spokeswoman for the Ganske campaign.says, “Harkin is so weak on the issue, he has to have Edwards go on the attack for him.”Warren says Ganske, as a member of the U-S House, has voted for a prescription drug benefit for Medicare, while nothing’s passed the Senate which is controlled by Harkin and other Democrats.