It’s easy to see why so many bright conservatives are talking up the idea: It’s one of the few free-market policies that would be guaranteed to have an immediate payoff in job creation. But if Republicans propose it, won’t they be pilloried for endangering Social Security and Medicare, which is what those payroll taxes are supposed to fund? Do any of the proponents of a payroll-tax cut — particularly those who see it as a smart political move by the Republicans as well as the right policy — have a solution to this problem?