Political scientist Brendan Nyhan has coined a mocking phrase (deriving from an earlier Matt Yglesias observation) to summarize this conventional wisdom: Political Green Lanternism. This refers to the famous DC Comics character who receives a power ring from aliens. The hook is that the ring derives its strength from the willpower of its bearer; a normal person won’t be able to accomplish much with it, but someone with strong willpower can all but move mountains.
Nyhan and others rely on some fairly recent political science literature suggesting that the presidency simply doesn’t work this way, and that the powers of the president to persuade are really much more limited than previously thought. The “great persuaders” were successful not so much because of their ability to wield the office’s clout, but rather were gifted with large partisan majorities in Congress and/or a public that was enthusiastically behind their goals.
My own view is somewhat hybrid, but leans more toward the poli-sci take on things: Give LBJ 234 Republicans in the House after the 1964 elections, like Obama has today (rather than the 140 Johnson had to contend with), and much of the Great Society doesn’t happen. Give FDR a bare majority of 220 Democrats in 1933, instead of 313, and much of the New Deal doesn’t pass. Indeed, Roosevelt had 334 House Democrats in 1937, and all it took was a recession to stymie his agenda. (FDR himself was partial to Green Lanternism, assuring nervous aides that once the letters of support started pouring in, opponents of the Third New Deal would be beating a path to the White House door.)