The bigger threat to same-sex marriage in Iowa next month may be the battle for control of the State Senate, where Democrats hold a one-seat advantage. Republicans have suggested that they would try to get a state constitutional amendment banning same-sex marriage on the ballot if they seized the majority. Supporters of same-sex marriage argue that the matter is one of equality and best decided by the courts; schools may have remained segregated and interracial marriages illegal if those issues had been left to popular votes, they say.