The fall of France came as a surprise to most people, so it stands to reason that not everyone saw the Allies' situation as dire as it was during the "Phoney War."
Churchill changed parties several times in his career. He had been responsible for some bad policies -- the Gallipoli campaign of the First World War, the botched return to the Gold Standard in 1925. The Norwegian campaign that led to Chamberlain's dismissal was also Churchill's idea.
We know now that Churchill was a great wartime leader, but there were plenty of reasons why his contemporaries didn't entirely trust him. And if his speeches were great, we know now that people with a reputation for great oratory don't always make great leaders.
I don't know how accurate it is, but it is well worth a read to get some different perspective on Churchill's rise to power.
In the book, it almost seems that Churchill didn't want to be PM if it meant kicking Chamberlain to the curb.
Anyway, fascinating read.
Great stuff...have fun!