For months, I've had no doubt whatsoever that Hillary Clinton planned to run for president in 2016. Anybody who watched her appearance at a campaign event in Iowa over the weekend probably saw their own such doubts disappear as well.

In that 20-minute speech, you could see Clinton beginning to hone the rhetoric and the issues that she expects to stress in the coming campaign. She talked of the importance of "shared opportunity and shared prosperity," of defending "families fighting to get into the middle class and families fighting to stay there." America needs leaders who understand the importance of reinforcing what she called "the basic bargain of America," she told the crowd of an estimated 7,000.

"You know what it is: No matter who you are or where you come from, if you work hard and you play by the rules, you deserve the same opportunity as everyone else to build a good life for yourself and your family."

It's an interesting framing of the issue. Clinton is clearly trying to raise issues of economic inequality while avoiding what Republicans would call "the politics of envy." Talking of "shared prosperity and shared opportunity" merely implies that someone might be taking more than their share, but implication is as far as she goes.

"It used to be that when productivity went up, wages went up," she said. "People could actually see all of that in their paychecks and feel it in their wallets. Today -- you know so well -- American families are working harder than ever but maintaining a middle-class lifestyle feels like pushing a boulder uphill every single day. That is not how it's supposed to be in America. This is the country, remember, where if you work hard you can make it, and each generation has done a little better than the one before. That is who we've always been, and that is who our country must be again."

Republican candidates will of course hit on similar themes -- declining median household incomes and the sense of a dimmer future that they inspire will be the single most important reality of the 2016 presidential campaign. And we know what their argument will be as well. The GOP explanation for our economic challenges won't focus on technological transformation or on structural changes in the global economy -- for the most part, they don't even acknowledge the existence of such factors.

Instead, their version of the domestic-policy agenda allows for only villain, which is government, and only one solution, which is less government. In that sense, at least, the GOP is easily the more government-centric of the two major parties. And while such monocausal explanations to complex phenomena don't offer much useful guidance in making policy, they do have the benefit of simplicity.

In politics, that's important.