Producer Robert Drew and his crew were granted unprecedented behind-the-scenes access to the Kennedy and Humphrey campaigns. Drew's use of innovative lightweight cameras and sound equipment allowed for an intimate, fly-on-the-wall style that was nearly unprecedented for documentaries of the day. The film is now regarded as a breakthrough in direct cinema and cinema verite filmmaking. Primary was added to the National Film Registry in 1990.
Drew followed up with the subsequent JFK documentaries Adventures on the New Frontier (1961), Crisis: Behind a Presidential Commitment (1963), and Faces of November (1964). The Criterion Collection released a DVD/Blu-ray set containing all four films in 2016.
- Book Ends: The first scene and the last scene are both Hubert Humphrey traveling the back roads of rural Wisconsin while his "Vote for Hubert" campaign jingle plays.
- Election Day Episode: How else would the movie end?
- Everybody Smokes: A woman introducing Kennedy at a rally in Milwaukee feels compelled to ask people in the crowd to stop smoking.
- Fish out of Water: The narration notes that eastern, urban, Catholic JFK is not a natural fit for small-town Wisconsin.
- Hitler Cam: Both candidates are shown this way on a couple of occasions.
- Minimalist Cast: A latter-day viewer might wonder why there are only two candidates for the Democratic nomination. The reason is that in 1960 only a few states conducted presidential primaries (fifteen states and Washington, D.C. for the Democrats) and most of the delegates to the nominating convention were still controlled by state party machines. The other main candidates for the 1960 Democratic nomination, Lyndon Johnson, Adlai Stevenson, and Stuart Symington, did not compete in any primaries. In fact, this primary and the later West Virginia primary were the only contested primaries of the campaign.
- Polka Dork: The kids playing an unbearably cheesy accordion arrangement of the Humphrey jingle as Humphrey shakes hands somewhere.
- Repurposed Pop Song: Frank Sinatra's "High Hopes" had an altered version used to promote John F. Kennedy for president, naturally the presidential version was used several times in the documentary in scenes with Kennedy.
- "Shaggy Dog" Story: Kennedy wins the primary, but he wins on what everyone already knew was his strength, namely, urban Catholic voters. Humphrey wins the rural Protestant regions of Wisconsin, and as the narration notes, the standings in the race remain unchanged after all that frantic campaigning. It was not this race, but Kennedy's easy victory the next month in heavily Protestant West Virginia, that proved the turning point in the campaign for the 1960 nomination.