According to the group Religious Tolerance, 90 percent of Americans disapproved of interracial marriage when it was first legalized by the California Supreme Court in 1948. Nineteen years later, when the U.S. Supreme Court legalized the practice, 72 percent of Americans still disapproved. The magical 50 percent threshold wasn't crossed until 1991-a change of 50 percentage points in 53 years. Coincidentally, people born in 1991 start voting next year.