Can the two parties adapt to the populism that's straining them before a third party rises?

Let’s stipulate up front that a serious third party isn’t likely to emerge, at least not in this cycle. A viable third party requires money and an outsize personality (think Ross Perot), and it isn’t clear those elements exist right now.

Still, it’s possible to see the ideological foundations for one. Similar populist refrains are coming from a diverse cast of political characters with real followings: Mr. Sanders and Sen. Elizabeth Warren on the left, and Rick Santorum, Mike Huckabee and Sen. Rand Paul on the right. Listen to the remarks of declared 2016 contenders and you can almost hear a potential third-party platform emerging. Here would be its main elements:

Big banks and Wall Street have too much power in Washington. “We have come to take our country back from the special interests that use Washington as their personal piggy bank,” Mr. Paul said in opening his presidential campaign. Said Mr. Sanders: “When we talk about power, we talk about Wall Street. In my view, it is time to break up the largest financial institutions in this country.”

The economic system is stacked against the middle class, and government policies are making that worse. In his announcement, Mr. Santorum referred to “workers” and “working families” a dozen times, and said they have suffered because of the policies of “big government and big business.” He has broken with GOP orthodoxy by supporting a “modest” minimum-wage increase and continuation of the Export-Import Bank to bolster manufacturing.