washington u.s. senate democrats defeat republican effort undercut iran nuclear agreement wednesday block amendment spend bill would stop obama administration buy heavy water tehran amendment energy spend bill offer republican senator tom cotton receive 57 yes vote 42 vote need 60 yes vote advance 100-member senate cotton withdraw amendment vote senate expect vote late version spend bill without measure would bar use u.s. government fund purchase heavy water non-radioactive use nuclear reactors make nuclear weapons last year nuclear deal iran unite state five world power tehran responsible reduce stock substance sell dilute dispose certain condition president barack obama administration warn congress strongly oppose move prevent plan purchase 8.6 million-worth heavy water iran senate democrats handful republicans also band together late april block cotton amendment hence spend bill dust-up put crimp senate majority leader mitch mcconnell plan pass bipartisan appropriations bill keep federal government function beyond sept. 30 end government fiscal year bid stop heavy water purchase iran block u.s. senate