Canada has had its own dark ages of anti-science politics under the government of Stephen Harper (2006–15). We at Evidence for Democracy, who led the fight against that ideology, offer these lessons to US scientists in how to protect scientific integrity under US President Donald Trump (see Nature 541, 435; 2017).

For more than a decade, scientists in Canada were muzzled, funding and research capacity were reduced and policy decisions were made in flagrant opposition of evidence. Scientists spoke out — and science has taken a prominent position since our last election.

We advise our US colleagues to document everything — every funding cut, every time a scientist is blocked from speaking to the media, every political interference in research. Meticulously logging such changes in Canada revealed that it was not a case of just a few cutbacks or isolated instances of gagging. An undeniable war on science was happening.

We recommend that scientists, especially in government, keep their data safe, record changes to communication policies and scientific integrity, and enlist support from international collaborators. These can intercede, catalogue your data and make your research publicly accessible.

Communication is key. It should be used to counter the real-life impact of withholding evidence from the public. To combat misinformation, the facts aren't enough; these won't necessarily change minds. Instead, tell stories that convey evidence and critical thinking: stories of how science has made all of our lives better.

What else? Rally behind US organizations such as the Union of Concerned Scientists; raise your media profile and engage politicians. Evidence has no ulterior political motives — that is the strength of our movement.