The importance of musical score
In the first season of S&H, you had Lalo Schifrin's dramatic theme song (and similar, heroic-sounding closing theme). And the episodic scores complemented it nicely during this, the show's most comparatively violent year.
In Season 2, you had the series' most famous theme, one by jazz musician Tom Scott, and, once again, the episodic scores fit nicely and helped drive the drama. Scott provided a number of those bouncy scores for Season 2 as well, as did MacLeod & Prigmore, Shorty Rogers, others.
The problems here began with Season 3...
For one thing, the show now adopted a much "jokier" opening theme design with countless shots of Glaser and Soul mugging for the camera (humor always worked best on STARSKY & HUTCH when it was in the background, as it was in Season 1). Season 3's new opening title visuals seemed to communicate the point that "see?, we really are a cartoon joke show after all...!"
Yes, violence restrictions were implemented across the industry effective fall of 1977, but doing a "comic" version of the titles was going way too far.
But then there was also the music. Mark Snow (later of X-FILES fame) composed the new atonal theme song for Season 3 (arguably, the show's worst theme music) but he also composed multiple episodic scores which were as atonal and drab as his new theme, if not more so.
These oft-tracked musical cues from Snow really slowed-down the drama during Season 3, helping take the air and the pacing out of the show and just served to underscore (literally) the program's reduction in action that year.
Then came Season 4: fortunately, Tom Scott's jaunty theme from S2 was back (although Scott contributed no new scores)... Unfortunately, even though his theme had now been replaced, they kept Mark Snow around as a frequent episodic scorist, causing many of the S4 instalments to suffer from the same ailment as those from S3: dryness and atonal drabness, killing much of the drama in an era of S&H when the limits on action needed to be countered any way possible.
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LBJ's mistress on JFK:
https://www.youtube.com/watch?v=WcXeutDmuRA