NBC’s recent decision to end the runs of “30 Rock,” “Parks and Recreation” and “Community” speaks volumes about the state of network viewership. Despite generating buzz, these highly rated series were not bringing in enough viewers.

For instance, the “30 Rock” season finale this year drew less than three million viewers. Twenty years ago, on the same night and the same network, “A Different World” was attracting an average of 14 million viewers per episode. And the American population is now about 25 percent larger than it was back then.

In political advertising, broadcast television has had pride of place ever since TV advertising began in the 1950s. Its preeminence can be found in its name, literally “broad cast.” With the ability to reach the entire electorate, political advertisers have been willing to go on broadcast even when rates were very high, and even if only a limited percent of a television market is relevant to the race.

But the advantages of the broadcast model have been breaking down for some time. Primetime viewership has been in a long, slow decline for decades. The primetime broadcast audience is about half of what it was 25 years ago. And during the same period, the amount of household televisions that are on during primetime has actually increased. So where are all the viewers going?

Cable, primarily. Primetime viewership of cable surpassed primetime broadcast viewership eight years ago. The ratings for the most popular cable series are now competitive with all but a few popular broadcast series and specials. The cable advertising philosophy has been targeting viewers by interest and by geography—the opposite of broadcast. This makes cable ideal for smaller scale races, but there’s still one major drawback to cable: not everyone has it.

The cable penetration in television markets ranges from anywhere around 85 percent in some big East Coast markets like New York and Boston to as low as 30 percent in some markets, particularly in mountainous areas. So even when cable programs have competitive ratings with broadcast shows, cable has still been at a disadvantage because its reach is much less than broadcast’s. And so even with all of the changes in the media landscape, political advertisers still devote most of their budgets in major races to broadcast.

The utility of both broadcast and cable advertising is being further undermined by TiVo, or what industry professionals call “time shifted viewing.” The current television ratings can now measure time shifted viewing within six hours of a program’s original airtime. This will capture viewers who watch a program later that night or who start watching a program a few minutes later to skip through all of the commercials. This is further decimating the effectiveness of political advertising, as skipped advertisements are wasted money.

One alternative has been digital advertising. Online budgets for most campaigns are still a small percentage of the overall budget, but are increasing. Online advertising can be targeted more efficiently—by, say, interest or geography—than cable.

Though Internet usage is now very high, the almost infinite number of web pages in existence means no web strategy can recreate the reach of broadcast. Digital advertising is more important than ever, but for political advertisers at least; it’s even less suited to replacing broadcast than cable.

In the near future, the balance of advertising budgets will likely be less strongly focused on broadcast. Major races that still spend 90 percent of their paid media budgets on broadcast are, in most cases, overinvesting in a medium that just cannot deliver as much as it once could. Look for the share of the advertising budget devoted to cable to increase. And as digital advertising becomes more sophisticated, it too will become more of a serious player in media buying decisions.

Chris Palko works as an assistant media analyst at Smart Media Group, a Republican political media buying agency in Alexandria, Va. He is a graduate of American University and George Washington University’s Graduate School of Political Management.

A version of this post was also published on Smart Media Group’s blog, Smart Blog.