@ GeorgesPlane- The current President Pro Tempore of the United States Senate is Daniel K. Inouye from Hawaii. If he should leave the senate for any reason while the democrats hold a majority, the next in line for the job would be Senator Patrick Leahy from Vermont. If the balance of power were to switch to the Republican Party within the senate, then the next President Pro Tempore would be Dick Lugar from Indiana. The next most senior republican senator after Dick Lugar is Orin Hatch from Utah. The majority and minority leaders of the senate are Harry Reid and Mitch McConnell respectively.