Los Angeles • Protestants, who have played a central role in the nation’s founding and development, no longer make up a majority of Americans for the first time in history, according to a study released Tuesday.

The study by the Pew Forum on Religion & Public Life found that Protestants now make up 48 percent of Americans, compared with nearly two-thirds in the 1970s and 1980s. The decline, concentrated among white members of both mainline and evangelical denominations, is amplified by an absence of Protestants on the U.S. Supreme Court and the Republican presidential ticket for the first time.