Wall Street will be listening closely to Federal Reserve Chair Jerome Powell's speech Friday at the Jackson Hole economic policy summit, where he could signal whether the central bank is ready to cut borrowing costs at its next meeting in September.

A potential candidate to succeed Federal Reserve Chair Jerome Powell, David Zervos, said that it’s inaccurate to describe the US central bank as independent, and characterized the outgoing Fed chief as aligned with the political left.

The U.S. dollar drifted on Thursday as investors fretted about the Federal Reserve's independence after yet another attack from President Donald Trump ahead of remarks from Chair Jerome Powell later this week that could influence the outlook for rates.