Could blood plasma be used to treat Covid-19?

What are we to make of the decision by the US Food and Drug Administration (FDA) to grant emergency use authorisation for blood plasma treatment of Covid-19? Is this a medical breakthrough or a dangerous move forced on it by a desperate president who sees his electoral chances slipping away unless he somehow gets on top of the crisis over the next few weeks?

It goes without saying that the approval of drugs ought to be above partisan politics.