When the great documentarian Errol Morris (“The Thin Blue Line”) has taken on overtly political subjects, he has rarely approached them from a position of express advocacy. His perspective tends to be more philosophical, even cosmic.

“American Dharma” (2019) sought to understand what made the former Trump White House strategist Steve Bannon tick. “Standard Operating Procedure” (2008) revolved around the photographs of Abu Ghraib prison in Iraq, and how acts that might look so obviously like torture were in certain cases rationalized as routine. The director’s portraits of former defense secretaries — Robert McNamara in “The Fog of War” (2003) and Donald Rumsfeld in “The Unknown Known” (2014) — centered on figures who were well out of office, even if, in 2003, McNamara’s reflections on the Vietnam War held up a clear mirror to Rumsfeld and his then-current approach to Iraq.

Morris’ “Separated,” on the Trump administration’s practice of taking children from their parents at the southern border, comes closer to a direct intervention. The filmmaker has been open about his desire to have it released before the presidential election, and although it is now playing in theaters, it isn’t set to air on MSNBC until Dec. 7, when its relevance will be reduced. “Why is my movie not being shown on NBC prior to the election?” Morris wrote on social platform X. “It is not a partisan movie. It’s about a policy that was disgusting and should not be allowed to happen again. Make your own inferences.”

If “Separated” is likely too straightforward — too much of a conventional issue documentary — to be remembered as one of Morris’ richest films, it is not as if the director has abandoned his sense of profound absurdity. In the film, Jonathan White, who worked for the Office of Refugee Resettlement within the Department of Health and Human Services when family separations began, speaks of a period in 2017 when those actions flew under the public’s radar. “It happened for months before there was any policy to do it,” he says, “and it was going on while my own leadership maintained it wasn’t.”

At the Venice Film Festival, Morris highlighted the contradiction: “If the purpose was deterrence, why do it covertly?” he said in August. (There is a hint of Peter Sellers’ Dr. Strangelove in that idea: “The whole point of the doomsday machine is lost if you keep it a secret.”) But White says that “harm to children was part of the point.”

White and Jallyn Sualog, who also worked for the Office of Refugee Resettlement, emerge as the standout interviewees in “Separated.” They come across as dedicated public servants who witnessed a horrifying shift in real time. Sualog says she became aware of separations when field staff started to notice very young children showing up. The children’s ages, and attendant inability to articulate information, posed an obstacle to reunification. “I’m not confident that we caught every single case,” Sualog says. The film cites a 2024 report from Homeland Security that puts the number of children who were separated from parents at more than 4,000.

The best that can be said of their vacant-seeming boss, Scott Lloyd, who ran the Office of Refugee Resettlement, is that it is unlikely he had ever heard of an Errol Morris movie before appearing in this one. NBC correspondent Jacob Soboroff, who serves as an executive producer on “Separated” and wrote a book of the same title, registers as more of a supporting player. At one point, he suggests that the Department of Homeland Security had sought to use his reporting as a tool for scaring migrants and pressuring Congress.

Morris’ customary use of dramatizations — in this case, to depict a mother and son experiencing the border crossing, separation and reunification — feels perfunctory this time. White’s fire, and his soaring warnings about how political sycophants willing to effect a policy like family separation will always exist, are powerful enough. If politicians “wish to use cruelty to achieve their deterrence ends,” he says, “such people will be found and such means will be ready at hand.”