It's interesting that trivia states Leffingwell or at least his "investigation" was based in some part on Alger Hiss.
Leffingwell is ultimately a hero in this story... Henry Fonda played him... how could he not be a hero? And to some extent I imagine Hollywood wanted to reinforce the left's defense of Hiss as a great American put upon by McCarthyism.
But the declassified Venona papers and admissions by soviet agents proved beyond a shadow of a doubt that Alger Hiss was a spy and a traitor to his country. For decades the left tried to defend him and bash the right for trying to take down such a "patriot". To this day there are still defenders who claim the evidence and witnesses are still "inconclusive"
I suspect at the time Hiss was still considered a true American. But in hindsight it is a tragic reality that so many in our government were blinded by their ideologies and couldn't see the danger Hiss presented to our nation just to protect "one of their own".
That being said... This is, in my opinion, one of the truly great political films ever made. Laughton, Pidgeon, and the supporting cast were superb. And it is probably one of the most authentic as to the inner machinations of our political system.
This sort of character assassination based on lies and hearsay is still in full bloom as we have been witnessing here in the past six months.
Leffingwell is ultimately a hero in this story... Henry Fonda played him... how could he not be a hero?
Leffingwell is certainly not a "hero" in this movie (and definitely not in the book). He's not a villain, just a man, with both good and bad in him. The fact that Henry Fonda played him is irrelevant -- Fonda played some less-than-heroic characters in his career. (And then there's Once Upon a Time in the West....) Kind of a silly comment.
While Allen Drury drew upon a few superficial aspects of the Hiss case in his book, Leffingwell is not Hiss. For one critical thing, Leffingwell didn't commit espionage, as Hiss did. Also, while Hiss went to prison for perjury there is no hint this will happen to Leffingwell. The "showdown" between Whittaker Chambers and Hiss did serve as a broad dramatic template for Drury's confrontation between Leffingwell and Herbert Gelman but you can't take the comparisons too far or too literally.
And to some extent I imagine Hollywood wanted to reinforce the left's defense of Hiss as a great American put upon by McCarthyism.
Interesting, considering that the film does anything but reinforce anyone's defense of Hiss (inferentially) or Leffingwell. Leffingwell is seen as someone who was stupidly involved with Communism as a young man but has long since quit the party. The only unlawful activity he engaged in is perjuring himself before the Senate Committee by denying he had known Gelman. (He was never asked if he'd been a Communist and so gave no answer, truthful or otherwise, to that issue.) Hiss was a longtime party member who unquestionably committed espionage, and lied about a great deal more before HUAC than the fictional Leffingwell did before the Senate committee.
Like a lot of people on all sides of the political spectrum who engage in broad-brush smears of people they disagree with, you falsely claim that "the left" uniformly defended Hiss. On the contrary, most liberals didn't think he was innocent, although some came to this realization only slowly over many years. As a lifelong liberal (well, moderate-liberal would be more accurate) I never thought Hiss was innocent and always believed he was guilty.
You also seem to have an uncertain grasp about "McCarthyism". The Hiss incident took place before the House Un-American Activities Committee in 1948 -- not the Senate, and nothing to do with Joe McCarthy, who didn't opportunistically jump aboard the anti-Communist bandwagon until 1950. Of course, you might be referring to the general confusion most people have concerning HUAC and McCarthy, but Hiss and McCarthy had nothing to do with one another.
Drury took elements of many real people and true incidents for Advise & Consent, most of which made it into the movie, but these were only cherry-picked aspects, not the full stories, and he shaped them for his novel. The gay-blackmail plot point about Brig Anderson had its origins in the actions of two Republican senators, Styles Bridges of New Hampshire and Herman Welker of Idaho, who blackmailed Senator Lester Hunt, a Wyoming Democrat, into retiring from the Senate in 1954 to give the GOP a chance to win Hunt's seat that fall. Hunt's son had been arrested in Washington, D.C., for soliciting gay sex and when the two senators found out about it they used it to force Hunt to retire, on pain of releasing it publicly. Hunt succumbed to this blackmail, but Welker and Bridges (sterling men of character that they were) reneged and let the news out anyway. Two weeks later Hunt shot himself in his office, hoping this would end the publicity about his son. This needless tragedy did the Republicans no good: though they got Hunt's seat by appointment for a few months, the Democrats recaptured it that November. And in a neat turn of justice, Welker lost his seat in 1956 and died the next year at 49, and Bridges died seven years later at 63. Cheats and liars ultimately never prosper.
People have all sorts of blinders on when it comes to their cherished political prejudices -- as your final statement about 2016 clearly demonstrates.