FDR dodged a coup or two from the upper crust, but he was also able to point to Russia 1917 and say, "you guys don't get on board or that's coming here." And he was right.
LBJ was destroyed, for the most part, by his own party's base. Nixon was Nixon.
Clinton was a master politician and excellent negotiator who played Gingrich like a violin. Obama is no Clinton.
People have moved to be closer to their ideological brethren. It has literally been a physical sorting process that began in the late 1960s.

