washington battle implementation iran nuclear deal erupt u.s. senate floor wednesday democrats maneuver block republican amendment stop obama administration buy heavy water tehran nuclear program vote 50-46 democrats four republicans band together stop fiscal 2017 energy spend bill order keep republican senator tom cotton offer amendment measure legislation need 60 yes vote move ahead president barack obama administration warn congress strongly oppose move prevent plan purchase 8.6 million worth 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 dust-up put crimp senate majority leader mitch mcconnell plan spend next several weeks advance bipartisan appropriations bill keep federal government function beyond sept. 30 end fiscal year vote senator chuck schumer senate democrat tell reporters democrats allow bill proceed potentially clear way vote cotton amendment republicans would embolden attach spend bill poison pill amendments white house oppose white house spokesman josh earnest say cotton focus undermine implementation nuclear deal iran administration gratify cotton amendment advance senate confident cotton differentiate heavy water sparkle water earnest said.cotton say want insure unite state taxpayer subsidize critical component iran nuclear industry would add require nuclear agreement iran every republican congress oppose nuclear agreement announce july join several obama fellow democrats trust tehran keep promise curtail nuclear program lawmakers try repeatedly pass legislation administration say would undermine mcconnell say would try pass spend bill accuse democrats find new ways blow appropriations process iran nuclear deal fight threaten senate spend bill