By DAVID CRARY, AP National Writer NEW YORK (AP) — The percentage of U.S. adults who belong to a church or other religious institution has plunged by 20 percentage points over the past two decades, hitting a low of 50% last year, according to a new Gallup poll. Among major demographic groups, the biggest drops were recorded among Democrats and Hispanics. Gallup said church membership was 70% in 1999