Donald J. Trump hasn’t done much TV advertising. He prefers a different style of campaigning, with rallies and the free media coverage of them, along with his frequent Twitter posts. Fund-raising has taken a back seat because, as Mr. Trump said: “I don’t even know why I need so much money. Why do I even need these commercials?”

With the election only a few weeks away, we’re about to find out.

Since June, there have been roughly 300,000 TV commercials on behalf of presidential candidates. Most of them have been in Florida, Ohio and North Carolina, but a small number have been on national networks. According to data collected by Kantar Media/CMAG, 80 percent of the ads to date were run by or on behalf of Hillary Clinton, while only 18 percent were shown by or on behalf of Mr. Trump. Nearly everywhere the race is competitive, Mrs. Clinton has run far more ads.

Most presidential campaigns are not like this. They are more like a tug of war with both sides pulling equally hard. The flag in the middle usually doesn’t move much, but that doesn’t mean pulling hard is a waste of effort — it’s just hard to tell, because one side’s effort cancels out the other’s.

But this year, one side has stopped pulling, giving us a rare chance to learn two things: whether all the effort exerted by Mrs. Clinton is moving the flag, and whether Mr. Trump’s method is a good substitute for a conventional ad campaign.