Hauser's Law
Some Republicans also rely on an argument dubbed Hauser's Law, named for W. Kurt Hauser, a former chairman of the Hoover Institution in California. He contended that the relative stability of the revenue-to-GDP ratio occurs because taxpayers react to higher taxes by underreporting income and shunning productive investments for tax shelters.
"That's where we've been historically, and that tends to be what our tax code raises," said Curtis Dubay, senior policy analyst at the Heritage Foundation, a Washington policy group that favors smaller government.
Hennessey, Burman and Viard said the consistency of revenues near 18% is more political than economic. When tax rates rise, the U.S. elects lawmakers who cut taxes, as when Ronald Reagan took office in 1981 and Bush did in 2001.
Viard said any increase in tax collections should be accompanied by changes to the tax system to minimize economic harm.
"If we're able to survive raising 19% of revenue from a badly flawed tax system," he said, "there cannot be any disaster from raising 20 or 21% from a better tax system."