Republican hardliners in Midwestern state governments have largely stalled efforts to modify marijuana laws there this year. But after more than a decade of pressure from grassroots activists, the region is beginning to show some change. The most dramatic advances have come in Michigan, where voters legalized medical marijuana in a 2008 referendum, and in Kentucky, which in early March reduced the maximum penalty for possession of less than half a pound from a year in prison to 45 days.