The most sweeping revision to the federal tax system was signed into law by President Donald J. Trump on Friday, and stock prices reacted by dropping a fraction. Why did the signing of the new tax law elicit a yawn from American investors?

Stock prices have soared all year, partly on expectations of a corporate tax break. The months of Washington, D.C. drama started last February 9 when President Trump promised a "phenomenal" new tax law, which was followed by a stock surge.

In September, after Republican House and Senate leadership announced an agreement with top Trump administration officials on a framework for the new tax law, stock prices surged again.