As the Stanford Encyclopedia of Philosophy discusses, one of the logical fallacies that we can find ourselves falling victim to as we try to navigate what is true in the world is an appeal to authority. Most of the time, this concerns a non-expert essentially masquerading as one in a field that they don't have as much expertise about as they may suggest.
After all, someone who has the right education and training should be a font of reliable information in an ideal world. However, appeals to authority can still be dangerous even when those qualifications are met because it's not impossible for perceived authorities to either intentionally or accidentally use their position to lend credence to false information.
Unfortunately, that's exactly the situation we face in the case of one doctor who has been elevated to prominence by President Donald Trump despite her habit of baseless claims.