The $64,000 question.
This idiom or expression like phrase means:
The main question.
An important question or issue.
When someone says “The economy is the $64,000 question,” they mean something like “It’s how we handle the economy that we should be talking about.”
Other numbers have been used also: The million dollar question, etc.
History:
The $64,000 Question was a television game show broadcast in the United States in the 1950’s, where the top prize was worth $64,000. What a surprise!