Janet Yellen was forced to fend off new questions about the Federal Reserve’s independence yesterday sparked by donations from a Fed governor to Hillary Clinton’s presidential campaign.

The Fed chair was challenged by Scott Garrett, a Republican congressman from New Jersey, over donations that Fed governor Lael Brainard has made to the Clinton campaign and over unconfirmed media reports that Ms Brainard was a contender for a senior job in a potential Clinton administration.

The exchanges came two days after Donald Trump, the Republican presidential candidate, claimed in his debate with Mrs Clinton that the Fed has been keeping short-term interest rates low to help the Obama administration and was sustaining a “big, fat, ugly bubble” in the stock market.