U.S. Treasury Secretary says there are many strong candidates for Fed chair, with the selection process starting this fall.  
Reports suggest Trump may nominate a successor earlier to limit current chair Powell's influence. His term has 11 months left.  
Trump could announce a replacement by Sept or Oct, possibly sooner due to his frustration with Powell.  
Potential picks include ex-Fed member Kevin Warsh and White House economic advisor Kevin Hassett. Others in the mix: ex-World Bank head Malp