Criminal investigations do not usually start with tweets. They very rarely start with tweets by government officials asserting someone’s guilt before a charge has even been laid. That, however, is how the case against Lisa Cook, a governor of the Federal Reserve, began on August 20th, when Bill Pulte, head of the Federal Housing Finance Agency, published a letter alleging that Ms Cook had “falsified bank documents and property records to acquire more favourable loan terms, potentially committing mortgage fraud”. Mr Pulte then tweeted a screenshot showing her signature on two documents. It is on the basis of this evidence that President Donald Trump sought to sack Ms Cook on August 25th. She has refused to resign; the courts will consider what is required to remove a Fed governor “for cause”.