(Bloomberg View) — America's convoluted tax code has needed comprehensive reform for years. The case for change would be open and shut even if families on low and middle incomes hadn't come under increasing strain of late — but they have. The middle-class squeeze underscores the need for a far-reaching overhaul.

The opportunity here is enormous, precisely because the tax system is so badly designed. If it weren't, making it better would involve difficult trade-offs: The price of a bit more efficiency might be a little less fairness, or vice versa. Happily, no such compromise is required. The system can be made fairer and more efficient at the same time.   

The crucial thing is simplicity. The last big tax reform, in 1986, broadened the tax base by removing or limiting exemptions for various kinds of income and spending, then used the proceeds to cut tax rates. This approach spurs efficiency in two ways. First, lower rates encourage people to work and invest; second, simplicity lets market forces, rather than the unintended interaction of complex preferences, guide choices. It's also more fair, because the tax breaks that Congress has added back since the last cleansing favor the most prosperous taxpayers.