We’ve been here before. With a week to go in 2012, President Obama’s campaign expanded where it was buying advertising, adding Pennsylvania and Michigan after weeks of no commercials, and Bill Clinton was dispatched to Pennsylvania to stump for Obama. At the time, some observers, especially hopeful Republicans, considered these moves a sign that Obama was on the defensive and that once-safe blue states might not be so safe. In the end, Obama won Pennsylvania by five points and Michigan by nine points.

Studies have shown that making advertising count depends on two criteria. The first is how close the ads air to Election Day. Again and again, researchers have found that ads’ effectiveness fades almost entirely within one week. Political strategists and operatives like to talk about early advertising “setting the tone” or “shifting the debate,” but there is no evidence to support any relationship between an ad a voter sees in June and the vote that person casts in November. Dropping one final big ad buy is simply smart strategy.

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The second criterion is how many more ads one side is running compared with the other side. The margin has to be large: One study found that in counties where Obama ran 2,000 more ads than John McCain in 2008, he gained just one point in the county over John Kerry’s 2004 total. Four years ago, Obama had the resources to effectively cancel out Mitt Romney’s late buys even in the safest states. Clinton has an even larger advantage over her opponent: Through the penultimate week of the election in 2012, Obama outspent Romney by almost $85 million. Going into 2016’s final week, Clinton’s advantage over Trump is $137 million. (Romney could count on outside spending to make up some of the gap; Trump can’t.) And in the final week, she’s nearly doubling his advertising spending. With Trump on the air in Colorado, New Mexico, Michigan and Virginia, Clinton would be foolish not to counter what he’s spending — and cancel out whatever advantage he might have gained — precisely because she can do so with plenty of money to spare.