President Trump sent the U.S. stock market on a jagged round trip Wednesday after saying he had “talked about the concept of firing” the head of the Federal Reserve. Such a move could help Wall Street get the lower interest rates it loves but would also risk a weakened Fed unable to make the unpopular moves needed to keep inflation under control.

This past April, when President Donald Trump started flirting with the notion of firing Fed Chair Jerome Powell, stocks and the dollar tumbled because investors worried that even talking about such a move crossed a red line.