WASHINGTON — On the evening of May 1, 1976, Ronald Reagan warbled the lyrics of The Eyes of Texas Are Upon You into a telephone from a hotel in Indiana. On the other end of the line, hundreds of Reagan revolutionaries in Houston burst into applause as the former California governor's rendition of the state song punctuated their giddy celebration of his 2-to-1 thrashing of incumbent Republican President Gerald Ford in that day's Texas presidential primary. Little did anyone at that Houston victory party know, but that moment would be a turning point not only for Reagan but also in...