The conventional wisdom among Donald Trump's supporters is that his success doesn't rely much on political ads. The evidence suggests otherwise. As Trump's ad spending has risen, the race has tightened. As it has dipped, his polling deficit has widened.
Over the past three months, according to the Associated Press's week-by-week tallies, Hillary Clinton has outspent Trump on television and radio ads by a total of $155 million to $19 million. Rounding to the nearest whole number, that's a ratio of 8-to-1.
But that ratio hasn't remained constant. From June 26 through August 20, Clinton ran $82 million in ads to Trump's $810,000—a ratio of 101-to-1. For a couple of weeks in early September, the gap closed to 2-to-1. Now it has widened back to 37-to-1. While Clinton has generally increased her spending by about 10 percent each week, Trump's spending has varied widely.
Perhaps most interesting is how the candidates' ad spending has correlated with the polls. The Real Clear Politics average of recent polls generally has about a one-week lag. For example, the polls on which the RCP average is currently based were taken mostly in the range of September 22 to September 30, with a midpoint of around September 26. Since the only ad that can affect a poll question asked on September 26 is one run on or before that date, the RCP average today is likely most heavily influenced by ads run during the week of September 18 to 24. So there's about a one-week lag between the end of a given week of ads and the polling average that will be most affected by those ads.
For the weeks ending on August 6, 13, and 20, Trump spent almost nothing on ads. Over that span, Clinton spent $36 million to Trump's $810,000—a ratio of 44-to-1. The RCP averages a week later in each case—on August 13, 20, and 27—found Clinton leading Trump nationally by between 5.5 and 7 percentage points.
Then Trump ramped up his ad spending. From August 21 to 27, Clinton spent $11 million on ads to Trump's $3.1 million—as he cut the ratio (again, rounding to the nearest whole number) to 4-to-1. A week later, on September 3, he had cut his deficit in the RCP average from 6.3 points to 3.9 points.
The following week, from August 28 to September 3, Trump further ramped up his ad spending and also widened the scope of his ads. Previously, he had adopted a rather defensive posture, running ads only in right-leaning Ohio, Florida, and North Carolina, and in one left-leaning state, Pennsylvania. During the week of August 28 to September 3, in contrast, he ran ads in essentially all of the important swing states. He ran ads in the states that are the keys to his five potential paths to victory—Virginia, Michigan, Colorado, New Hampshire, and Pennsylvania—as well as ads in Nevada, Iowa, Ohio, Florida, and North Carolina. Clinton spent $10.7 million on ads that week to Trump's $4.8 million, as he cut the ratio to 2-to-1. A week later, on September 10, he had cut Clinton's lead in the RCP average to 2.7 points.
The next week, from September 4 to 10, was Trump's most aggressive week of ad spending to date. Clinton ramped up her ad spending, as well, to $14 million, but Trump spent $7.3 million—keeping the ratio at 2-to-1. Trump ran ads in the same 10 states as the week before, but this time he actually outspent Clinton in Colorado and New Hampshire, as well as in Virginia and Michigan (two states in which Clinton hasn't run ads since August 13—or, in Michigan's case, at all). A week later, on September 17, Trump had cut Clinton's lead in the RCP average to just one point.
All of the momentum was on his side, yet Trump pulled back. During the next two weeks, from September 11 to 24, Clinton outspent Trump $37.1 million to $3.2 million—a ratio of 12-to-1. Moreover, Trump returned to his mostly defensive posture of running ads only in Ohio, Florida, North Carolina, and Pennsylvania. During the most recent week for which tallies are available, September 18 to 24, Trump ran fewer than one percent as many ads as he'd run just two weeks earlier, getting outspent 37-to-1 ($19.3 million to $516,000) in the process. In that week, Clinton spent more in New Hampshire ($706,000) than Trump spent nationwide. She spent more than twice as much in Nevada ($1.3 million), and almost 10 times as much in Florida ($5.1 million), as he spent from coast to coast. A week later, on October 1, her lead was back up to 2.7 points.
The great unknown is what will happen going forward. Trump has been raising a fair amount of money. Not the favorite candidate of the donor class by any means, he has racked up a near-fortune in small-dollar donations (in the ballpark of $100 million). As of the end of August, Trump reportedly had about three-quarters as much cash-on-hand as Clinton (although her Super PAC is far more potent than his). He shouldn't continue to get outspent 8-to-1 or worse.
The question that may decide this presidential race is this: Has Trump wisely been waiting for the stretch run and is now poised for an October ad blitz designed to open up all five of his potential paths to victory? Or is Trump saving his money for … well, for who knows what?