The Supreme Court has just begun hearing arguments in cases from Kentucky, Michigan, Ohio and Tennessee which could expand the rights of same-sex couples to marry. Over about 2-and-a-half hours, the justices will hear arguments centered on two questions: does the 14th Amendment require a state to issue a marriage license to two people of the same sex?; and, must states that forbid such unions recognize valid same-sex marriages issued elsewhere? As NBC News's Pete Williams explains, the court will be deciding what the states must do, not what they may do. A decision is not expected until June.