This year’s presidential political conventions are unprecedented in at least two unfortunate respects: the inclusion of a political film that’s negative, not positive, and the decision, by the broadcast networks, to show fewer convention hours than ever before…

The two events are not directly connected, but both are symptoms of a changing tide that has all but washed away the value of watching democracy in action on our country’s most democratic, widespread medium.

To chart this changing tide, we have to look at what’s happening right now — with TV’s coverage plans for the 2012 Republican National Convention, as well as Citizen United’s anti-Barack Obama film — and contrast it with the very beginning, and the evolving history, of broadcast coverage of political conventions.

Let’s start with the current stuff, then flash back to the past.

Friday night on Fox News Channel’s Hannity program, Sean Hannity played host to the three men responsible for the polling, interviewing and/or filmmaking regarding The Hope & the Change, an anti-Obama movie interviewing Democratic and independent voters who had voted for the President in 2008, but have soured on him since. (Later in the show, Hannity interviewed seven of those voters in a mini-focus group.)

Hannity also interviewed the trio responsible for the Citizens United film — producer David Bossie, writer-director Steve Bannon, and Fox News contributor Pat Caddell, a consultant on the 60-minute movie — with questions that were even tougher on Obama than anyone in the movie.

“I’m almost convinced,” Hannity told his Citizens United guests, talking about the faithful Obama supporters, “that if we had Barack Obama on tape, you know, robbing a bank and shooting all the tellers, they’d say, ‘Well, that’s okay, because we’ve got to give that money to the poor.’ There are some people who have never woken up from that trance.”

Pollster Caddell, who recruited and questioned those disaffected middle-class voters shown in The Hope & the Change, told Hannity, “This is the voice of the people who will decide this election.” He may well be right. And Hannity, for one, was about as impressed by the film as one could get.

“This is the most powerful documentary I’ve ever seen in my life,” Hannity said at the start of his program.

Others, regardless of their political leanings, may disagree with that unabashed orgasm of praise — excerpts from the movie shown on Hannity, with its succession of talking heads with their personal complaints, made it seem less like The Sorrow and the Pity than The Narrow and the Petty.

The artistic quality of The Hope & the Change, however, is almost beside the point. The point, instead, is that this film — anti-Obama, rather than pro-Mitt Romney, or even pro-Republican — is scheduled to appear during Tuesday night’s official presentation at the Republican National Convention. That hasn’t ever happened before.

Previously, on those occasions on which outsiders were asked to produce films for convention use (as when Harry Thomason, far right, and Linda Bloodworth-Thomason produced The Man from Hope, a Bill Clinton biography for the 1992 Democratic National Convention), the results were glowing tributes to that party and its candidate — not an attack on the other side.

It’s my opinion, as a TV critic, that both extremes can teach us something, and that even the most orchestrated moments in a political convention can reveal a great deal about each party’s approach, intent, and level of blatant manipulation. But the more television turns itself away from these conventions, or segregates its coverage to cable outlets already leaning towards one political party or the other, the less the TV viewer is truly served, at a time when television could, and should, be more important than ever.

For 2012, the commercial broadcast networks are presenting less prime-time coverage of the Republican National Convention than ever before, and presumably will follow suit for the Democrats next month.

CBS, NBC, and ABC are avoiding Monday’s events altogether in prime time, and are allotting only the 10-11 p.m. ET hour for convention coverage on Tuesday through Thursday. Fox is letting Fox News handle things, but through the prisms of their regularly scheduled prime-time shows and hosts. Ditto for MSNBC, and, for the most part, CNN. So if you want live, as-it-happens coverage of the conventions, the place to go is PBS on broadcast TV, and good old, invaluable, wholly impartial C-SPAN on cable.

But it wasn’t always like this. Reputations used to be made covering political conventions — the very term “anchorman” was coined to describe Walter Cronkite’s duties for CBS at the conventions of 1952 — and broadcast networks competed to provide more, not less.

Initially, network coverage of political conventions was experimental, trying out new media (radio in 1924, TV as far back as 1940). Then it was promotional, with manufacturers of television sets underwriting often gavel-to-gavel coverage: CBS and DuMont’s coverage was fully sponsored by Westinghouse, NBC’s by Philco, and ABC’s by Admiral.

In 1968, the demonstrations and police brutality outside the Democratic National Convention in Chicago told the real story of that divisive year — and after that, both parties were much more careful in controlling their televised images, in and beyond the convention halls.

By 1980, both political parties had wised up, and began orchestrating events to include “spontaneous” displays by delegates and carefully controlled speeches and presentations. But even then, analysts such as Bill Moyers for CBS were given the air time, and the trust, to put things in perspective. After that, though, the networks all began to cut back on the amount of coverage, once it could be seen on C-SPAN, CNN and elsewhere.

So now, in 2012, we’ve gotten to the point where CBS, NBC and ABC are offering a total of three hours of coverage over four nights. Comedy Central’s The Daily Show with Jon Stewart is offering more than half that, all by itself. And, I’m not joking, viewers can probably learn more there, from Stewart and company, about what’s actually happening on the convention floor.

It’s not too much to ask that our commercial TV networks, with their broadcast licenses and frequencies provided by the people, strip two weeks’ worth of prime-time programming every four years to let us watch our political candidates and parties in action. It’s almost too little to ask.

And to those who say the whole thing’s propaganda now, and nothing but a dog-and-pony show, I say that each party reveals a lot by parading its particular dogs and ponies — the vitriolic The Hope & the Change, for example, rather than the 2012 equivalent of The Man from Hope.

And if the broadcast networks want to argue that the prime-time real estate they’d be giving up for political coverage is far too valuable, they abdicated that argument long ago. What, after all, would we Americans be sacrificing during those precious 8-10 p.m. summer hours?

Bachelor Pad. Stars Earn Stripes. America’s Got Talent. Big Brother. And Wipeout.

I’m just saying: Pre-empting those shows would be a valuable public service in and of itself.