>> reporter: ronald reagan talked about arms control and summoned vigorous praise for the pontiff. >> in your travels you've inspired millions, people of all races and all faiths. >> reporter: george w. bush did the same. >> his holiness, pope john paul ii, has championed the cause of the poor. >> reporter: only to be criticized for looking too casual when he met john paul's successor, pope benedict. some meetings have been relatively short, some surprisingly long. but all are unique such as when barack obama noted pope francis is not merely a great man of peace but also a funny one. >> i can't share all his jokes. they were all clean. [ laughter ] >> reporter: so it is that these meetings are always a peculiar blend of piety and politics between two of the most influential souls on the planet. with both knowing the whole world is watching.