Wall Street Journal op-ed, The Revenue Limits of Tax and Spend: Whether Rates Are High or Low, Evidence Shows Our Tax System Won’t Collect More Than 20% of GDP, by David Ransom:

The nearby chart shows how tax revenue has grown over the past eight decades along with the size of the economy. It illustrates the empirical relationship first introduced on this page 20 years ago by the Hoover Institution’s W. Kurt Hauser—a close proportionality between revenue and GDP since World War II, despite big changes in marginal tax rates in both directions. “Hauser’s Law,” as I call this formula, reveals a kind of capacity ceiling for federal tax receipts at about 19% of GDP.