That position, created in the Constitution, is to be filled by the Senate's longest-serving member of the majority party -- in this case, Senator Daniel Inouye (D-Hawaii): Daniel Inouye Succeeds Robert Byrd As Senate President Pro-Tempore, Third In Line Of Presidential Succession.
Sen. Daniel Inouye (D-Hawaii), now 85 years old and a 47 and a half year Senate warhorse, now takes that honor and is expected to be sworn in at 2 p.m. Monday.Sen. Inouye, who was first elected in 1962, was sworn in as president pro tem when the Senate convened this afternoon: Inouye Sworn In as President Pro Tem. After his swearing in, he briefly presided over the floor as senators spoke about Byrd. More here: With Sen. Byrd's death, Inouye now third in presidential succession.
Inouye was elected in 1962 and is currently serving as chairman of the Senate Appropriations Committee, a position that he acquired from Byrd after the late Senator stepped down due to health concerns. According to the Presidential Succession Act, Inouye will be placed behind Vice President Joseph Biden and House Speaker Nancy Pelosi in the line of presidential succession.