Having all but tamed inflation, the Federal Reserve is poised to do something on Wednesday it hasn’t done in more than four years: Cut its benchmark interest rate, a step that should lead to lower borrowing costs for consumers and businesses just weeks before the presidential election. And yet an unusual air of uncertainty overhangs this week’s meeting: It’s unclear just how large the Fed’s rate cut will be. Wall Street traders and some economists foresee a growing likelihood that the central bank will announce a larger-than-usual half-point cut. Many analysts foresee a more typical quarter-po…