Among white Democrats, Obama’s job approval rating has dropped 11 points since his 100-days mark in April, according to surveys by the Pew Research Center for the People and the Press. It has dropped by 9 points among white independents and whites over 50, and by 12 points among white women — all groups that will be targeted by both parties in next year’s midterm elections.

“While Obama has a lock on African Americans, his support among white voters seems to be almost in a free fall,” said veteran Republican pollster Neil Newhouse.

Strategists in both parties blame Obama’s decline on growing discontent with his policy agenda, particularly after a month of often-rowdy debate over his proposed healthcare overhaul, in which some conservatives accused him of socialism. Obama’s ratings seem likely to rise again if he wins passage of healthcare legislation this fall.