The U.S. Chamber of Commerce has more than doubled its spending on political attack ads since Tuesday, prompting criticism from liberal groups that question the origin of the funds. The chamber reported spending $9.3 million on ads targeting Democrats in eight Senate and 22 House races since Tuesday. It had spent just less than $9 million this year through Monday. Chamber President Tom Donohue has pledged to spend $75 million this election season as the business group tries to oust Members who voted for policies it opposes, such as the health care and financial regulatory overhauls.