Presidential candidate Sen. Ted Cruz (R-TX) speaks while Carly Fiorina (L) and New Jersey Gov. Chris Christie looks on during the CNBC Republican Presidential Debate. (Photo by Justin Sullivan/Getty Images)

From July 2 through October 29, Donald Trump had an amazing run: Every single day, he was mentioned more on cable news channels than any other Republican candidate for president. It was rarely even close. Since Trump entered the GOP race in mid-June, he has accounted for nearly half the TV news coverage of the GOP field, according to data compiled by the Internet Archive and curated by the GDELT Project.

That coverage is immensely lucrative in a campaign where, despite record-breaking fund-raising hauls, candidates have frequently risen and fallen based on their use of what's called "earned media" -- the stories and airtime you don't have to pay for.

There's no question that Trump has played the earned media game masterfully. We can quantify just how masterfully by comparing the news coverage data with polling data over the past year, as compiled by Real Clear Politics. It's clear from the data that TV news coverage over time tracks largely, but not entirely, with candidates' relative positioning in the polls. The better a candidate is polling, the more air time she or he tends to get.

Some candidates, though, get more coverage than their poll numbers suggest they should. Some candidates get a lot less. The outliers raise interesting questions about media fairness. Those questions go well beyond Trump; lately, he's not even the biggest overachiever on the air.

Also, Ted Cruz has real cause for complaint.

Here's a chart showing a breakdown of candidate polling performance and television mentions so far this year. The green bar shows a candidate's average percentage of support in the polls compiled by Real Clear Politics for their polling average. The blue bar shows the candidate's share of all on-air mentions for GOP candidates on national cable networks this year.


Source: Real Clear Politics and the Internet Archive.

Those numbers show us that Trump and Jeb Bush snag way more TV time than their polling would appear to merit - 90 percent more for Trump, about 70 percent more for Bush. On the flip side, Cruz and Rand Paul receive about 60 percent fewer mentions than their polling would suggest, and Mike Huckabee gets about 70 percent less. (In percentage terms, the biggest over-performer is Lindsay Graham, though he barely registers on either metric.)

Now here's the same chart for the past month:


Source: Real Clear Politics and the Internet Archive.

Trump's media over-performance has shrunk by more than half, to 40 percent. That reflects his reduced air time recently; a different candidate has scored more time than he has on five different days since Oct. 30. Bush's overperformance has ballooned, to 177 percent. That may reflect a lot of stories about the trouble in Bush's campaign, or it may reflect a brewing comeback narrative, but either way, it's way out of line with what other candidates are experiencing.

Paul and Huckabee are still underperforming, and Ben Carson remains far behind Trump despite near-tied poll numbers, but Cruz has the biggest bone to pick. He's on the air 70 percent less than his polling would suggest, even as he's climbed past Bush and into fourth place in the race.

We'll leave it to you to debate what's going on here with Bush, Trump and Cruz (and for those inclined to suggest ideological bias, we'd note that the gap for Cruz looks just as bad if you only look at the data for Fox News).

There's a bigger question to debate, too: What should determine which candidates get covered on TV? Polls? Entertainment value? Ratings? A public service mission to help voters make choices in a crowded field? It's an important question, and the answer makes a huge financial difference in the race.