This is extraordinary - we've never seen anything like this in central banking. Powell is essentially accusing the president of extortion.

Republican Senator Tom Tillis said he won't support any Fed chair nominee until this matter is resolved, making it difficult for Trump to nominate a loyalist.

Markets are reacting negatively because they don't want the president messing with the Federal Reserve's interest rate setting.

This subpoena raises questions about who could be next Fed chair - likely someone less connected to the Federal Reserve if Trump views it as corrupt.