kennedy and the other far older one perpetuated by joe biden. cnn's tom foreman explains. ♪ >> reporter: when the first catholic president met pope paul vi tensions were rife. the italians loved john kennedy while conservatives back home wondered if he would bow to religious tradition and kiss the pontiff's ring. kennedy shook hands, and the potential clash vanished. u.s. presidents have been meeting popes for just over a century. each encounter closely watched for friendship and friction. when lyndon johnson and richard nixon discussed the vietnam war in separate meetings with pope paul, the conversations reportedly grew heated. john paul ii was the first pontiff to visit the white house, where he and jimmy carter, a devout protestant, found common ground. >> we share a belief that the church must in no way be confused with the political community nor bound to any political system.