Four years later, Chisholm would make history again, as the first African American woman to run for president. That campaign is the focus of “Shirley,” written and directed by John Ridley, who does a dutiful job of laying out the dynamics of the race to defeat Richard M. Nixon, a Democratic primary that included initial front-runner Edmund Muskie, as well as Hubert Humphrey, John Lindsay, George Wallace and the eventual nominee, George McGovern.

Chisholm’s slogan was “Unbought and Unbossed”; she was also constantly underfunded and underestimated by the political structures she was forced to navigate, whether it was factions led by such leaders as Congressional Black Caucus founder Walter Fauntroy (played with smirking condescension by André Holland) and Black Panther Huey Newton (Brad James) or White feminists. “Shirley” includes a snippet of Gloria Steinem saying she supported McGovern as the most acceptable White male candidate; what it fails to mention is that Steinem raised money for Chisholm in the states in which she ran, and wrote the speech she gave after being cut out of a televised debate.

Such are the nuances left on the cutting-room floor of a movie that feels perfunctory and starchily instructional when it should be a stirring monument to one of the most consequential figures of America’s 20th century. Constructed with episodic predictability graced with a few expressionistic flourishes, “Shirley” co-stars Christina Jackson as Chisholm’s protégé Barbara Lee, who would represent her own 12th District as a U.S. representative of California; Lee appears late in the film to reinforce Chisholm’s importance as a transformational politician, but none of that juice animates the preceding drama. (Viewers interested in Chisholm’s life and career will find a terrific primer in Shola Lynch’s 2004 documentary “Chisholm ’72: Unbought and Unbossed.”)

Lucas Hedges, Terrence Howard and the late Lance Reddick — appearing in his final role — portray the men who rallied around Chisholm during a run that looks quixotic, then hopeless, until a suspenseful sequence involving delegate horse-trading at the Democratic National Convention in Miami Beach; but it’s King who gives “Shirley” its spirit and soul, inhabiting Chisholm with a steely confidence that is only somewhat disguised by her gentle Barbadian accent.

King’s Chisholm is so wise, so graceful (her visit to Wallace after an attempt on his life is particularly moving), that it’s easy to see why both her opponents and allies chronically misjudged and patronized her. Even at its most staid and dramatically inert, “Shirley” leaves no doubt that they did so at their peril.

PG-13. At Landmark’s E Street Cinema; available March 22 on Netflix. Contains profanity including racial slurs, brief violence and some smoking. 117 minutes.