Hillary Clinton’s campaign ran TV ads that had less to do with policy than any other presidential candidate in the past four presidential races, according to a new study published on Monday by the Wesleyan Media Project.

Clinton’s team spent a whopping $1 billion on the election in all — about twice what Donald Trump’s campaign spent. Clinton spent $72 million on television ads in the final weeks alone.

But only 25 percent of advertising supporting her campaign went after Trump on policy grounds, the researchers found. By comparison, every other presidential candidate going back to at least 2000 devoted more than 40 percent of his or her advertising to policy-based attacks. None spent nearly as much time going after an opponent’s personality as Clinton’s ads did.

Trump, who didn’t exactly run as a wonk, aired a more typical number of policy-focused ads compared with past elections. As an example, the study notes his first big TV buy was for an ad called “Two Americas” — one that portrayed life under Clinton’s immigration policies and one under Trump’s. The Clinton world is pretty bleak. Trump’s is rosy. In all, Factcheck.org gave it a so-so review, saying the claims were based on “murky evidence and misrepresentations.”

Beyond overall ad spending, the study also breaks down the content of the attack ads aired on behalf of each candidate. It says about 70 percent of Trump’s ads “contained at least some discussion of policy.” About 90 percent of Clinton’s attack ads went after Trump as an individual — compared with just 10 percent that went after his policies, the study found.

The study concludes that Clinton’s strategy may have backfired badly. Here’s what they have to say:

Evidence suggests that negativity in advertising can have a backlash effect on the sponsor (Pinkleton 1997) and that personally-focused, trait-based negative messages (especially those that are uncivil) tend to be seen as less fair, less informative and less important than more substantive, policy-based messaging (Fridkin and Geer 1994; Brooks and Geer 2007). In stark contrast to any prior presidential cycle for which we have Kantar Media/CMAG data, the Clinton campaign overwhelmingly chose to focus on Trump’s personality and fitness for office (in a sense, doubling down on the news media’s focus), leaving very little room for discussion in advertising of the reasons why Clinton herself was the better choice. Trump, on the other hand, provided explicit policy-based contrasts, highlighting his strengths and Clinton’s weaknesses, a strategy that research suggests voters find helpful in decision-making. These strategic differences may have meant that Clinton was more prone to voter backlash and did nothing to overcome the media’s lack of focus on Clinton’s policy knowledge, especially for residents of Michigan and Wisconsin, in particular, who were receiving policy-based (and specifically economically-focused) messaging from Trump.

Of course, as Vox’s Tara Golshan has pointed out, Clinton’s team likely pursued this line against Trump because they thought it was working — most of the polling suggested Clinton was going to win on Election Day.

But the new report also confirms what multiple outlets have already reported: that the Clinton campaign did not appear to realize its vulnerability in the Rust Belt until the final days of the election and, as a result, blew millions that could have been spent elsewhere. Clinton’s team spent virtually nothing advertising in Wisconsin, Michigan, or Pennsylvania until the final week — when they then decided to exponentially increase their resources there.

The Wesleyan researchers write, with some understatement:

[I]t may very well be that Clinton misallocated advertising funds (both hyper-targeting on local cable and advertising in non-traditional battlegrounds like Arizona rather than in the Midwest, for example) and a lack of policy messaging in advertising may have hurt Clinton enough to have made a difference.

The blown money on TV advertising in Arizona was exacerbated by a ground strategy that local Rust Belt Democrats have heavily criticized. As Sen. Gary Peters (D-MI) told Vox in December 2016, the Clinton campaign appeared to do little to relate to Midwest union workers in the runup to the vote:

As far as I know, she didn’t stop at any UAW halls. I probably would have been invited to be with her if she was going to one, and I never got that invitation. She didn't do any labor-specific events that I'm aware of. It's pretty rare that you aren't working closely with labor in a campaign, especially for statewide office. I'm sitting right here now, talking to you in the parking lot of the sheet metal workers before their holiday party. I'm going to be with my friends, with the sheet metal workers, to convey that they are important to me by showing up at their events. Labor simply cannot be taken for granted in Michigan. Not doing that sort of event certainly was a major oversight.

The new study was conducted by Erika Fowler, a Wesleyan government professor; Travid Ridout, a philosophy and public affairs professor at Washington State University; and Michael Franz, a government and legal studies professor at Bowdoin College. You can read it in full here.