Reaching those conclusions, however, can be a bit of a challenge for two reasons. One, which we won't really go into here, is that some policies that are now disfavored were put in place while Republicans were in charge of the national pandemic response. This leads to a number of awkward juxtapositions in the report: Operation Warp Speed is praised, while the vaccines it produced can't really be trusted; lockdowns promoted by Trump adviser Deborah Birx were terrible, but Birx's boss at the time goes unmentioned.

That's all a bit awkward, but it has little to do with evaluating scientific evidence. Here, the report authors' desire to reach specific conclusions runs into a minefield of a complicated evidentiary record. For example, the authors want to praise the international travel restrictions that Trump put in place early in the pandemic. But we know almost nothing about their impact because most countries put restrictions in place after the virus was already present, and any effect they had was lost in the pandemic's rapid spread.

At the same time, we have a lot of evidence that the use of well-fitted, high-quality masks can be effective at limiting the spread of SARS-CoV-2. Unfortunately, that's the opposite of the conclusion favored by Republican politicians.

So how did they navigate this? By shifting the standard of evidence required between topics. For example, in concluding that "President Trump’s rapidly implemented travel restrictions saved lives," the report cites a single study as evidence. But that study is primarily based on computer models of the spread of six diseases—none of them COVID-19. As science goes, it's not nothing, but we'd like to see a lot more before reaching any conclusions.

In contrast, when it comes to mask use, where there's extensive evidence that they can be effective, the report concludes they're all worthless: "The US Centers for Disease Control and Prevention relied on flawed studies to support the issuance of mask mandates." The supposed flaw is that these studies weren't randomized controlled trials—a standard far more strict than the same report required for travel restrictions. "The CDC provided a list of approximately 15 studies that demonstrated wearing masks reduced new infections," the report acknowledges. "Yet all 15 of the provided studies are observational studies that were conducted after COVID-19 began and, importantly, none of them were [randomized controlled trials]."