Update: As my esteemed colleague Dr. J-Rob has pointed out, it is Keith Poole, not Ken Poole
Mark Hatfield, a former Senator from Oregon, died yesterday. He was one of those Republicans who don't exist anymore.
As the obituary notes, he increasingly became more and more out of step with his caucus. Let's look at Keith Poole's lifetime numbers. Poole's scoring is from -1 to 1, with -1 being the farthest left, 1 being the farthest right
Early in his career, in the 92nd Congress, he was the Republican with the 6th most liberal lifetime score from Keith Poole, behind Jacob Javits, Edward Brooke, Clifford Case, Charles Mathias and Lowell Weicker (who at the time was, albeit a bit more conservative). 3 other Republican Senators had lifetime scores less than; Robert Stafford, Richard Schweikert and Charles Percy. 6 more had lifetime scores between 0 and 0.1; Marlow Cook, John Sherman Cooper, George Aiken, Hiram Fong, Bob Packwood, Margaret Chase Smith and Marlow Cook.
In his last term, he was the Republican with the most liberal lifetime score. Only 3 others had lifetime scores of less than 0 (Jeffords and Specter, who later quit the party, and John Chafee, whose son Lincoln, who basically followed in his footsteps, also quit the party). Only 3 others had lifetime scores between 0 and 0.1 (Cohen, Packwood and Snowe [although Snowe may not anymore since those numbers are from 2004]).
In the 92nd Congress, Ted Stevens' lifetime score (up to 2004) of .183 placed him in the center of the Republican caucus (22nd most liberal of 45 Senators [including Prouty who died mid-Congress]). By the 104th Congress, Stevens was the 10th most liberal Republican out of 56.