Over the past two weeks, Biden had the airwaves to himself in Iowa, Ohio, Texas and New Hampshire, while Trump went dark, according to Advertising Analytics, a TV tracking firm. This week, Trump isn’t airing any ads in Nebraska, where both campaigns are competing for the lone Electoral College vote out of the Omaha-based congressional district, while Biden is dropping just under $500,000.

The spending disparity isn't limited to Democratic "reach" states. Biden and his allies are also racking up ad advantages in the core battlegrounds that put Trump in the White House in 2016. Biden is out-advertising Trump in 72 out of 83 media markets where the campaigns are spending this week, including dozens of places that played a critical role in deciding the last election, like Philadelphia and Wilkes-Barre in Pennsylvania and Milwaukee and Green Bay in Wisconsin.

Republican super PACs are making up some of the gap, but Democratic ones are still outspending their counterparts in more media markets, too.

Trump’s TV spending problems stem from his fundraising woes. At the end of August, Biden had more money to spend than Trump — the first time that's happened during the 2020 campaign. The Democrat smashed fundraising records with a $365 million haul that month, beating Trump’s total by over $150 million.

Neither campaign has released their fundraising totals for September yet. But a person familiar with the total confirmed to POLITICO that Biden is expected to beat his own August total.

The fact that Trump “doesn’t have enough money to compete in a fundamental swing state like Iowa tells you they’re really stretched thin from a financial perspective,” said Ken Spain, a former National Republican Congressional Committee spokesman. “[Biden’s campaign] capitalized on its momentum, raised money in late summer, spent it strategically, and that’s translated into a bump in the polls, which in turn, brings in more money for them. That’s a troubling sign [for the Trump campaign].”

In addition to Texas, the Biden campaign is also investing in earnest this week in Ohio, the perennial battleground state that Trump won by 8 points in 2016.

The Biden campaign declined to comment. In a statement, the Trump campaign said it wasn't concerned with Biden's spending in those and other states.

"President Trump and our campaign are extremely confident about states like Texas, Ohio, and Iowa," said Trump campaign spokeswoman Courtney Parella.

Biden’s campaign is spending $1.4 million in Ohio this week and just over $1 million in Texas, according to ad-tracking data from Advertising Analytics. Both states — especially Texas — are big enough to swallow up a lot more money than that, but it’s notable because of what Trump is spending in response: nothing.

While Biden expands the battleground map, Trump and the GOP aren’t chasing the Democratic campaign. That's because they've already fallen behind in TV advertising in the states mostly likely to decide whether he wins or loses, such as Michigan and Pennsylvania. But even in those states, Biden is still outspending Trump two- or even three-to-one on TV ads over the last few weeks.

In Pennsylvania, where Biden has spent $17 million in the last three weeks to Trump’s $7 million, Democratic outside groups have poured in another $14 million on top of that, while GOP groups have put in $8 million.

In Florida, where Trump is doing his biggest TV spending, he’s still falling behind, spending $17 million to Biden’s $20 million over the last three weeks. Democratic outside groups are also beating their Republican counterparts by a similar spread.

“In any campaign where you’re being outspent, you need to focus your spending and you can’t be spread thin, and so they’re continuing to make their bets on Pennsylvania, Michigan and Wisconsin,” said Mike DuHaime, a national Republican consultant. “The Trump campaign would rather be outspending Biden two-to-one than the other way around, and there’s no doubt that matters.”

“It’s not ideal,” DuHaime added, “but it makes sense.”

Countless political candidates have won races despite being out-advertised, including Trump in the last presidential election. But 2020 is a different race, and Trump is trailing in the polls by a more meaningful — and stable — margin than he did before his 2016 victory.

It’s not impossible that Trump could win a second term despite trailing now, but he is running out of time to turn his campaign around. And while TV advertising is only one component of a campaign — albeit the most expensive one — the advertising situation is another headwind for his reelection. The others: his Covid-19 diagnosis and public disapproval of his handling of the pandemic, his low overall job performance numbers, and his conduct in his first debate against Biden.

Political ads make the most difference when one side is able to air more of them — and especially when a party gets the opportunity to make their argument unanswered. That can drive movement in the polls or help a candidate over-perform those polls in the election results.

Biden’s advertising totals in some places, including Ohio, look smaller compared to Trump’s in the final weeks of the election, according to the TV ad reservations both campaigns have laid down. Trump is slated to spend $2.5 million there next week, for example, while Biden only has $1 million reserved.

But those reservations may be misleading for two reasons: Trump’s campaign has been canceling reservations week by week in Ohio, New Hampshire and a handful of other states. Biden has been building up his ad budget as his campaign continues to rake in millions of dollars online.

GOP outside groups, led by Preserve America, have been making up some of the difference. But outside groups — whether it's the pro-Trump Preserve America or America First Action, or Mike Bloomberg’s Independence USA PAC — operate at a key disadvantage to political campaigns. Federal law says that candidates get to pay the “lowest unit rate” to buy their ads on local TV stations, but the stations and the market set the rates higher for outside groups.

That means super PACs’ millions buy fewer ads. And it's why Biden’s fundraising edge has turned into such an important advantage.