Next week, President Obama is scheduled to propose new measures to boost the economy. I hope they’re bold and substantive, since the Republicans will oppose him regardless — if he came out for motherhood, the G.O.P. would declare motherhood un-American. So he should put them on the spot for standing in the way of real action. But let’s put politics aside and talk about what we’ve actually learned about economic policy over the past 20 months. When Mr. Obama first proposed $800 billion in fiscal stimulus, there were two groups of critics. Both argued that unemployment would stay high —...