U.S. Treasury Sec. Yellen 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 counter Powell's influence. His term has 11 months left.  
Trump could announce a pick by Sept. or Oct., possibly even sooner due to his frustration with Powell.  
Potential candidates include ex-Fed governor Kevin Warsh, NEC director Kevin Hassett, and others like ex-World Bank chief Malpass or Fed governor Wall