U.S. President Donald Trump has named four people for two seats on the Federal Reserve's board of governors. None of them have made it through the Senate, raising doubts about the president's central bank acumen and the White House's vetting process for nominees.

Conservative economic pundit Stephen Moore on Thursday was the latest Fed candidate to flame out, following businessman Herman Cain and economists Nellie Liang and Marvin Goodfriend.

Moore's exit, following weeks of questions about his qualifications and criticism of his past writings and public remarks, renewed frustrations among Republicans and the president's own advisers that the White House's nomination process is light on background research and driven largely by Trump's whims. Trump, meanwhile, failed in trying to place political loyalists on the Fed's board and may be forced to consider more conventional candidates.