Massachusetts, the first state to legalize gay marriage, yesterday became the first to challenge the constitutionality of a federal law that defines marriage as the union of a man and a woman, contending that Congress intruded into a matter that should be left to states. The suit filed by state Attorney General Martha Coakley says the Defense of Marriage Act of 1996 violates the US Constitution by interfering with the state’s right to define the marital status of residents. The suit also says the law forces the state to discriminate against same-sex married couples - on certain health benefits and...