The independence of central banks, which allows policymakers to operate free from political meddling, is considered sacrosanct by investors and economists.

Three things can simultaneously be true: that it would be reasonable for the Federal Reserve to cut interest rates; that its headquarters renovation is too expensive; and that the Trump administration's attacks show why central banks are designed to be independent in the first place.

US President Donald Trump this week escalated attacks on central bank chair Jerome Powell, suggesting he could be dismissed for "fraud" over his handling of a renovation project at the Federal Reserve's headquarters.