President Donald Trump made a promise at a reception last week for Republican lawmakers that was as impossible as it was specific: He would drive down drug prices by as much as 1,500 percent — “numbers that are not even thought to be achievable,” he said. A price cannot drop by more than 100 percent, but Trump went on to make several other precise but clearly false numerical claims. The cost of gasoline had fallen to $1.99 a gallon in five states, he said; according to AAA, it was over $3 in every state. Businesses had invested $16 trillion in...