Bavarian elections threaten to further shake Europe's established order

There is little to mark the border between Germany and Austria at Kiefersfelden besides a European Union flag and three bored But this may be starting to unravel for Angela Merkel's Bavarian allies.

Bavaria votes on Sunday in regional elections. Mrs Merkel's regional sister party has ruled Bavaria since 1957, but if the polls are right, the Social Christian Union (CSU) faces a fight to hold onto power.

For once, the threat is not a populist revolt. Instead, the CSU appears to have self-destructed in its attempts to head off a challenge. Horst Seehofer, the CSU leader, …