Trump. Photo: Joe Raedle/Getty Images

Since the end of the primary season, America’s presidential candidates have spent $100 million on television advertisements. The Republican nominee, however, hasn’t spent a penny.

According to NBC News, Hillary Clinton has plowed $52 million into general-election TV spots, while Donald Trump has allocated a mere $0 to such things. That puts him far behind Libertarian nominee Gary Johnson and Green Party standard-bearer Jill Stein, who have spent $15,000 and $189,000 on ads, respectively. (Pro-Trump outside groups have spent $8 million on ads, but that’s still a fraction of what Clinton’s super-pacs have spent.)

The fact that the GOP nominee is being outspent on the airwaves by his Green Party rival is bizarre for several reasons. For one, Trump has plenty of money to spend: Last week, his campaign announced that it had raked in $82 million in July.

For another, the past two weeks have provided ample evidence that Trump’s campaign can’t live on free media alone. The GOP nominee’s decision to attack the bereaved parents of an American war hero helped him dominate the news cycle. But not all publicity is good publicity, at least if you want to win a presidential election: In the wake of the Khan-troversy, Trump’s poll numbers have plummeted, with many national surveys showing Clinton ahead by double digits.

What’s more, as the Washington Post’s Philip Bump notes, the longer Trump waits to buy ad time, the more expensive it will be. As any deal-maker knows, a rare commodity is a pricey one. And by the time his fellow presidential hopefuls — and other down-ballot politicians — reserve their ad time, there will be precious little remaining for the Republican standard-bearer.

Finally, there’s little evidence that Trump has opted out of the air war for the sake of maximizing his investment in field operations. “I can honestly say I have never seen a Republican presidential campaign with this weak of a field presence,” one Florida Republican told Politico in early June.

All of which raises the question: What exactly is Trump spending his money on? We’ll have to wait for the campaign’s July spending report to know for certain. But in June, Trump’s biggest spending category was “fundraising consultants.” Which makes some sense, since his fundraising over the first half of this year was dismal.

He also spent a lot on advertising that month, although strictly in the digital realm, putting $1.63 million into online ads — four times as much as Hillary Clinton did over the same period. Trump also invested $29,000 in Facebook advertising in June. Which is roughly 15 percent of what the campaign spent on branded trucker hats in May.

Regardless, Trump has a lot of money and plenty of ground he needs to make up. Why his campaign isn’t using that money to tell its story during purple states’ commercial breaks is a mystery.