Wrong as usual
https://en.wikipedia.org/wiki/Robert_Byrd and let me quote :
"As the longest-serving Democratic senator, Byrd served as President pro tempore four times when his party was in the majority:from 1989 until the Republicans won control of the Senate in 1995; for 17 days in early 2001, when the Senate was evenly split between parties and outgoing Vice President Al Gore broke the tie in favor of the Democrats; when the Democrats regained the majority in June 2001 after Senator Jim Jeffords of Vermont left the Republican Party to become an independent; and again from 2007 to his death in 2010, as a result of the 2006 Senate elections. In this capacity, Byrd was third in the line of presidential succession at the time of his death, behind Vice President Joe Biden and House Speaker Nancy Pelosi."
"On May 19, 2008, Byrd endorsed Barack Obama (D-Illinois). One week after the West Virginia Democratic Primary, in which Hillary Clinton defeated Obama by 41 to 32 per cent, Byrd said, "Barack Obama is a noble-hearted patriot and humble Christian, and he has my full faith and support." When asked in October 2008 about the possibility that the issue of race would influence West Virginia voters, as Obama is an African-American, Byrd replied, "Those days are gone. Gone!"Obama lost West Virginia (by 13%) but won the election.
On January 26, 2009, Byrd was one of three Democrats to vote against the confirmation of Timothy Geithner as United States Secretary of the Treasury (along with Russ Feingold of Wisconsin and Tom Harkin of Iowa)."
So Byrd is clearly a democrat not a republican.