Donald Trump still hasn't spent a dime on commercials, but he promises to start

With less than three months until the election, Donald Trump's presidential campaign has still yet to spend a dime on TV commercials.

The sum -- or lack thereof -- was confirmed in a recent update from NBC News and tracking firm Advertising Analytics, which have been jointly charting spending throughout the election cycle.

The few pro-Trump TV spots that have aired came from assorted PACs and outside groups, which have spent a combined total of $12.4 million on the Republican nominee's behalf.

By contrast, Mitt Romney's 2012 presidential campaign had racked up bills totaling nearly 20 times as much by this stage in the election -- about $233 million. And that doesn't even account for the $90 million kicked in by his biggest surrogate PAC.

Even long-shot candidates Jill Stein, the Green Party hopeful, and Libertarian nominee Gary Johnson have plunked down more than Trump, with ad budgets of around $189,000 and $15,000 respectively.

Meanwhile, Democratic nominee Hillary Clinton has been making up the difference. Her campaign has shelled out around $61 million thus far to own the airwaves -- on top of $43 million from outside groups.

Trump's absence from commercial breaks makes even less sense when you consider that his campaign raised about $82 million last month, finishing out July with $74 million in the coffers.

However, the divisive nominee has had trouble fundraising in the past, and his scrappy campaign has operated on a shoestring budget for its entire existence.

Nonetheless, Trump said on Tuesday that he would at last start buying TV time in some battleground states this week.

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Like much of what Trump does, the decision to skip TV for so long flies in the face of conventional political wisdom.

The celebrity-mogul managed to coast through the primaries on the cheap thanks to an outsized presence on political talk shows and round-the-clock coverage of his frequent spats and outlandish antics. The media's insatiable appetite is estimated to have earned him nearly $2 billion in free air time.

Trump's relative success led some pundits to hastily question the effectiveness of political advertising as a whole, a notion that Trump himself encouraged.

"You almost say, do ads mean anything?" the candidate said back in May, voicing a hypothesis that several media watchers had also put forth. "I think we're going to hurt the industry pretty much because people are going to say, 'What does an ad mean?'"

But such a sweeping pronouncement ignores the quirks that make Trump's presidential run such an outlier, some doubtful theorists say.

"Skeptics have persistently overlooked the elephant in the room: Trump is a TV celebrity," wrote Mark Lieberman, CEO of media analytics firm Tivo Research, in a recent op-ed. "'The Donald' had the benefit of more than a decade of weekly primetime TV exposure."

Another wrench in that logic: News coverage of Trump has taken a decidedly sour turn in the weeks following his coronation in Cleveland. The gaffes that once seemed to ricochet off his bullet-proof support base are now tanking his poll numbers.

Trump's perceived inability to stick to any semblance of a driving message has been the subject of much hand-wringing among GOP figures these past few weeks.

That's exactly the sort of thing that political advertising is meant to buttress -- it allows for the crafting of a controlled narrative free of the editorial spin of media coverage.

Research shows that the impact of political advertising is generally muted and fleeting, UCLA political communications professor Lynn Vavreck writes in the New York Times. But it is nonetheless still necessary for well-oiled campaigns in search of that extra bit of edge on an opponent, she continues.

Trump hasn't been sitting out the advertising churn completely; his campaign has dropped relatively small sums on digital ads, including promoted Twitter hashtags (#TrumpIsWithYou and #GetYourTrumpGear) with six-figure price tags. Trump even outspent Clinton on digital marketing in June with expenses of $1.6 million on online ads and digital consulting, according to the campaign's Federal Election Committee filing.

This strategy actually matches a bigger trend in political spending. While TV is still dominant, more and more ad money has been trickling into digital mediums in recent elections. A report from research firm Borrell Associates last year predicted this election cycle would yield record-high online spending.

That forecast seems to be just about the only one that's held true this election season.