Although both are founding members of Turkey's ruling party, increasingly the two men appear to be at odds with one another on a variety of political issues. The rivalry could have far-reaching consequences for the country. The Turkish president, Abdullah Gul, has in the past few months been challenging what is perceived as the increasingly tough positions of the prime minister, Recep Tayyip Erdogan, whether on the treatment of the country’s Kurdish minority, imprisoned journalists or advocating membership in the European Union. Last month Erdogan voiced his frustration. He said Turkey is not ruled by double-headed governance and he said...