There's almost nothing about his actual politics.
I'm a communist. Let me state that first of all so that there's no confusion as to me being anti-Trumbo, anti-communist or agreeing with the blacklist or anything.
But, as a communist, I rented this documentary in part because I was interested in learning about that side of Trumbo. The 2015 movie barely touched on it. This documentary touched it even less. The closest it came was when a letter to the telephone company was recited in which Trumbo said something to the effect of "when we reds come to power, we're going to shoot the capitalists in the following order" and went on like that, which was no doubt rhetorical, but he at least outright said he was a "red", something the documentary otherwise avoided addressing. In fact, I believe that was the only confirmation in the entire film that he was a communist.
The whole documentary was framed as being about the personal struggle of those who were blacklisted, which is interesting and relevant but only part of the story. The story was told from a liberal humanist point of view of people's individual struggles against the violation of abstract "rights", and Trumbo's resistance to the McCarthyites, not as reactionaries, but as "heavy-handed government" intruding on people's private lives.
I found this hole in the story really disappointing. I learned far more about Trumbo's views on masturbation than his views on capitalism, communism, class struggle, imperialism, the Cold War, the Soviet Union or Stalin. Which were the sort of things I was hoping to hear about. Frankly I don't understand why the masturbation stuff even needed to be included. Why were his views on masturbation more relevant to the story than his views on communism, and why was it was so important to include the former while the latter had to be completely discarded?
Maybe the liberal filmmakers wanted to downplay the radical side of Trumbo because it would make it harder for a non-communist audience to identify or sympathize with him; they wanted the whole thing to be a "human struggle" that anyone can get behind, rather than a political, revolutionary struggle. But in doing so, I think they're ultimately letting the McCarthyites win. The McCarthyites didn't just want to crush "freedom of thought" in general and for its own sake, but to destroy communism and make it inconceivable for anyone in the US to be a communist. In sweeping the communist views of Trumbo under the rug to make him palatable to liberals, the people telling his story are really playing the same game as those who tried to suppress him by coercion. Simply erasing the revolutionary struggle he and other communists were engaged in. Whitewashing them and reducing them to abstract icons of individual heroism against government tyranny and witch-hunt politics. One would think they had no political views at all before McCarthyism.
I think they do a disservice to Trumbo by going about it this way. Of course he had to be secretive about being a communist in his lifetime, in the climate he lived in, but there's no reason to hide it now other than to continue the McCarthyite goal of eradicating communism, now purging it even from memory.
This also misrepresents what McCarthyism actually was. It wasn't some unhappy accident that spun out of control, the product of the mindless "hysteria" of irrational people who were just intolerant of other people's personal opinions. McCarthyism was the entirely rational campaign of a reactionary ruling class to eliminate threats to its power. The class system they represented was being overthrown in one country after another. The Soviet Union terrified the bourgeoisie and the governments it ruled for the same reason revolutionary France once terrified the kings and aristocrats of Europe. The McCarthyites saw communism, not as a threat to the PEOPLE of the US (whom they were happy to trample upon to eradicate the communist idea from their midst), but as a threat to THEIR SYSTEM of power, privilege and private accumulation of wealth on the backs of the laboring class. In fact, what the US government feared most was not the Soviet Union itself (which could never have invaded the US and had no desire to do so), but the ideas the Soviet Union inspired in other people, including the people of the US, tens of thousands of whom did become communists and probably millions of whom became sympathetic to communism. In the final analysis, what the capitalist government of the US feared most was its own population, the working class of its own country, whom they feared would rise up against their class.
By presenting McCarthyism as an isolated period of hysteria with no real cause and no one to blame, we fail to learn its real lessons and fail to see its real cause. McCarthyism was not a one-time thing. It happened in many countries, some far more violently than others. And it will happen again any time a capitalist government is threatened by its own working class.