Peter Boyle and Allen Garfield
It seems every decade in Hollywood brings not only a new crop of leading men and leading ladies, but a new crop of character actors.
In 1972, two of the best were Peter Boyle and Allen Garfield.
Boyle came into "The Candidate" having played the scary killer hardhat in "Joe" (1970) and was two years away from his most famous movie role in "Young Frankenstein"(1974.)
Boyle was a coupla DECADES away from his most famous TV role on "Everybody Loves Raymond," where he was good but reduced by looking tired and aged for the run of the show(because he was.)
But in "The Candidate," we get Peter Boyle young and vital and acerbic and crafty (and thickly bearded) and its a great performance, as his wily political mentor slowly and carefully lures the "good" Robert Redford from the virginity of political idealism ("You Lose") into the thickets of political "reality." Is Boyle a bad man here, or a good man...out for money, out for power, out to do good? He keeps it crafty to the very, very end.
Allen Garfield specialized at the time in fast tawkin', gum chewin', fast hustlin' con man characters back then. He eventually got too old to play them for the laughs he needed to get, but here and in "The Conversation" two years later, he's at the top of his game. If Peter Boyle is "gently mentoring" Redford away from his ideals, Garfield is hitting him with a slap in the face(funniest: Garfield showing Redford the disastrous tape of his attempt to talk at a health clinic.)
By the way, just to show how "the same character type plays through time" in Hollywood, modernly you could use Paul Giamatti in Garfield's role here with ease.
Indeed, Giamatti played a political guy in Clooney's "The Ides of March" opposite the late great Philip Seymour Hoffman as ANOTHER political guy....
...and probably Hoffman in his prime could have played Peter Boyle's role here.