Some people are too open for their own good. That was certainly how I felt after interviewing Samantha Power last week.

I had expected her, as a senior adviser on foreign policy to Barack Obama, to be ultra-careful and to weigh every word. Not at all. She was open and amusing, willing to give long discursive answers on controversial subjects, happy to admit to doubts about her abilities to do a government job. I was charmed. But I left the lunch wondering whether she was really cut out for politics.