Wisconsin Gov. Scott Walker, seizing the moment after the Supreme Court’s landmark ruling legalizing same-sex marriage, called Friday for a Constitutional amendment that would allow the states to decide whether gay marriage should be legal. Walker’s call came shortly after the high court ruled 5-4 that same-sex couples could marry across the country, overturning a number of state same-sex marriage bans. The ruling was “a grave mistake,” the Republican governor said, touting his support for amending his state’s constitution “to protect the institution of marriage from exactly this type of judicial activism.” “As a result of this decision, the only...