Donald Trump officially nominated Kevin Warsh to lead the Fed, sending the nomination to the Senate to replace Jerome Powell.Senator Thom Tillis vowed to block the confirmation until a federal criminal investigation into Jerome Powell's $2.5B renovation project is dropped.The probe, involving Senate testimony and office upgrades, follows intense pressure from the White House on the central bank to lower interest rates.Kevin Warsh, a former Fed governor and Stanford University fellow, faces a difficult path due to the narrow Republican majority in the Senate.