Pope Francis in America: Pontiff's message on climate change and immigration leaves Republicans wrong-footed

For a couple of days at least, the world’s lone superpower has a new master. Not an embattled Democratic president, nor a bickering Republican-led Congress, but a 78-year-old Argentine, visibly suffering from a touch of sciatica and with a fragile command of the local language, the latest ruler of an earthly kingdom of just 109 acres on the other side of the Atlantic.