Among the many mysteries in the Donald Trump phenomenon, the question of his campaign spending is perhaps not the most pressing, but it is among the most inscrutable.

On Tuesday, Trump told reporters in New Hampshire that he was going to start buying ads soon. “Starting around January 4 we're spending a lot of money,” he said. “We are gonna spend a lot of money over the next four weeks, we don't want to take any chances. We are too close.”

Imagine that! Trump saying the polls were close. (He’s not wrong: He now trails in Iowa, though his lead in New Hampshire remains robust.) Trump didn't give a dollar amount, but Howard Kurtz reported Monday that the campaign would spend $2 million per week and perhaps more. This is all assuming the ads really materialize. In August he was said to be on the verge of spending millions on advertising in early primary states, but it never actually happened. Instead, he dropped just $300,000 on some radio ads.

But why now? There’s little reason to doubt Trump’s stated reasoning: The early-state primaries and caucuses are getting close, Trump’s leads are either gone or precarious, and it’s the right time to spend. The question is why he didn’t do so earlier. The standard explanation is: Why bother? Trump has done so well earning media—i.e., capturing press attention—that it doesn’t even seem worth the trouble and cost to pay for it. The second is one that Trump likes to cheekily deliver:

He noted in another tweet that his campaign was $35 million under budget. But the image of the Trump campaign as a model of financial frugality and rectitude is undercut by the fact that—as Tim Fernholz spotted—he’s paying about a quarter of his campaign expenses to himself, in the form of payouts to his own companies.

Fernholz wryly notes that Trump suggested in 2000, during an earlier presidential flirtation, that he could be the first candidate to make a profit on a campaign. But what if that really is what’s going on? One of the other mysteries of Trump’s spending is that despite his nearly constant mentions that he’s self-funding his campaign, it’s not really true. While Trump isn’t holding fundraisers in the traditional sense—no bundlers, no $2,700 per plate dinners, no multimillionaire-backed super PACs—he is taking in money in the form of donations, whether as cash or as payment for those confounded "MAKE AMERICA GREAT AGAIN” hats. Fernholz writes:

Trump loaned his campaign just over $1.8 million during the second quarter of this year, but as of Oct 1. his campaign had spent $5.4 million. Most of the balance, $3.9 million, came from donors. Some contributions are “unsolicited,” in Trump’s words, but the rest comes from buying merchandise or clicking on the large “donate” buttons on his website.

The new, alleged ad blitz shows that while Trump has managed to defy the rules of politics as conventionally understood, his campaign still believes there’s value in broadcast advertising. (The campaign didn’t respond to a request for comment by the time of publication.)

And that’s the biggest mystery of all. Since a few million dollars is basically chump change to Trump, why hasn’t he been more willing to open up his wallet earlier? If Trump is unable to seal the deal in the Republican primary, it probably won’t be because of lack of support—it will be because of lack of reliable polling, get-out-the-vote efforts, advertising, and the like. If he loses out on the nomination for lack of willingness to spend, Trump will come off looking penny-wise and pound-foolish.