Mr. Romney’s position on the Bush tax cuts, which reduced the top marginal rate for the wealthiest Americans to 35% from 39.6%, is likewise unclear. During his a stop in Berlin, N.H., on Tuesday, he spoke favorably of the Bush tax cuts. But as governor of Massachusetts, Mr. Romney refused to endorse them. As the Boston Globe reported in 2003, Mr. Romney told the state’s congressional delegation that he didn’t support tax cuts for the wealthy and wouldn’t be a “cheerleader.” By the time Mr. Romney was running for president four years later, he’d come around to supporting the tax cuts.

His stance on reforming the tax code to make it flatter and more efficient is also murky.