<Tr> <Td> </Td> <Td> Kenneth McKellar </Td> <Td> January 3--20, 1949 </Td> <Td> President pro tempore </Td> </Tr> <Tr> <Td> </Td> <Td> Alben W. Barkley </Td> <Td> January 20, 1949--January 20, 1953 </Td> <Td> President of the Senate </Td> </Tr> <Tr> <Td> </Td> <Td> Richard Nixon </Td> <Td> January 20, 1953--January 20, 1961 </Td> <Td> President of the Senate </Td> </Tr> <Tr> <Td> </Td> <Td> Lyndon B. Johnson </Td> <Td> January 20, 1961--November 22, 1963 </Td> <Td> President of the Senate </Td> </Tr>

Who is the presiding officer of the united states senate