The Presidential Premise
Recently, I overheard somebody crediting the economy's strength to the president. Under Donald Trump, the argument ran, businesses have recaptured their "animal spirits" and are acting with renewed confidence, which has stimulated job creation, thereby sparking the stock market. In addition, companies are benefiting from January's tax cut.
Such claims are difficult to corroborate. Nobody measures the animal spirits of corporate executives, nor can the effect of a single factor on the economy be readily judged. Even if U.S. job growth had accelerated since January, it would be speculative to credit that change to the tax bill. It is more speculative yet when such an event has not occurred.