Once upon a time, I might've said John McCain, but he vacillates too much between being a so-called "maverick" and a loyal drone who dutifully toes the party line. Jeff Flake from Arizona has been steadfast in his opposition of Orange Foolius, but he's quitting, beyond him, I can't think of too many who have the gravitas in the GOP, not to mention the balls to stand up to Trump without getting trounced by Turtle Boy and Eddie Munster, not to mention Faux News.