A column in the Wall Street Journal discusses Senator Obama’s plan to boost the top tax rate on entrepreneurs and investors from less than 38 percent to more than 50 percent. This huge tax increase will significantly undermine incentives to both earn and report income. As a result, the author, formerly with the Social Security Administration, explains that behavioral responses will result in far less money than projected by “static” revenue estimates:

Mr. Obama has recently veered sharply left. He now proposes to solve the looming Social Security shortfall exclusively with higher taxes. …Currently, all wages below about $100,000 are subject to a 12.4% Social Security payroll tax. But all wages above that amount are not subject to the tax. Mr. Obama wants to eliminate the cap, but, in a concession to taxpayers, exempt wages between $100,000 and $200,000. …Mr. Obama’s plan would keep Social Security in the black for only three additional years. Under his proposal, annual deficits would hit in 2020, instead of 2017. By the 2030s the system would still run an annual deficit exceeding $150 billion. Mr. Obama’s modest improvements to Social Security’s financing come at a steep cost. …The top marginal federal tax rates would effectively increase to 50.3% from 37.9%, equivalent to repealing the Bush income tax cuts almost three times over. If one accounts for behavioral responses, even the modest budgetary improvements from Mr. Obama’s plan are likely to be overstated. If employers reduce wages to cover their increased payroll‐​tax liabilities, these wages would no longer be subject to state or federal income taxes, or Medicare taxes. A 2006 study by Harvard economist and Obama adviser Jeffrey Liebman concluded that roughly 20% of revenue increases from raising the tax cap would be offset by declining non‐​Social Security taxes. Assuming modest negative behavioral responses, Mr. Liebman projected an additional 30% reduction in net revenues, leaving barely half the intended revenue intact. Mr. Obama’s plan would also dramatically raise incentives for tax evasion, further degrading revenue gains. Many high‐​earning individuals evade the Medicare payroll tax by setting up “S Corporations,” paying themselves in untaxed dividends rather than taxable wages. John Edwards avoided $590,000 in Medicare taxes this way in the 1990s. …The U.S. already collects far more Social Security taxes from high earners than other countries do. Social Security taxes here are currently capped at about three times the national average wage — far above other developed countries. In Canada and France payroll taxes are levied only up to the average wage. In the United Kingdom, taxes stop at 1.15 times the average wage; in Germany and Japan at 1.5 times.

Obama also wants to let the Bush tax cuts expire, which means the top tax rate would rise even farther — to more than 55 percent. But the bad news may get even worse. It is unclear how Obama will “fix” the alternative minimum tax. If his Social Security plan is any indication, he may propose to raise the top rate even further. What would all this mean? Simply stated, European‐​style tax rates will mean European‐​style stagnation.