Republicans love to invoke Ronald Reagan and for good reason. He won the White House by unseating an incumbent president, not easy to do. But in this race, none of the candidates has managed Reagan’s signature political feat.

He united the two disparate and often quarreling camps of the right — social conservatives and economic conservatives. That split has been on stark display throughout the GOP primary campaign.

Mitt Romney represents the economic conservatives. Sort of. The series of not-Mitt candidates, with the exception of Ron Paul (in a different orbit entirely), have competed for the social-conservative vote.

So what you had in Iowa was Romney and the latest not-Mitt — Rick Santorum — finishing almost dead even. The GOP remains badly divided.

The categories mentioned above aren’t bright lines. There’s significant overlap between the economic and social threads. The difference is largely found in emphasis and implicit priorities.

For Santorum, the future is all about the family. For a strong national economy, “we must have strong families,” he says. He wants faster economic growth not as an end in itself, but to buttress the family. More telling, writes David Brooks of The New York Times, Santorum isn’t above “picking fights” with supply-siders, the core of the GOP’s economic-conservative wing.

For Romney, economic growth is presented not only as an end in itself, but as the seedbed of renewal and innovation — as the way to open the door to a brighter future.

Romney can deliver the entrepreneurial vibe but he has a maddening tendency to hedge. His economic plan is a 59-point hodgepodge. He will push for lower taxes, less regulation, more drilling. All well and good, but this is a classic example of Churchill’s pudding that has “no theme.” Compare Romney’s pudding to the central element of Reagan’s economic platform — a 30-percent across-the-board tax-rate cut.

In a recent Wall Street Journal interview, Romney even refused to rule out a value-added tax. A VAT is the dream of every liberal desperate for the revenue needed to finance the goal of changing America into a sluggish European welfare state.

Let’s note that neither Romney or Santorum won high marks from the Tax Foundation for their economic plans. Romney was given a C-. He offered “no step toward fundamental reform,” nor would his plan reduce the tax code’s complexity, the analysts concluded.

Santorum got a D: No reduction in complexity. His idea of deep tax breaks for manufacturing businesses would add complexity.

Yet if the nomination fight remains murky for some time, Romney and Santorum (assuming he remains the not-Mitt) will have time to hone their platforms and presentations. Romney needs to find clarity, while fighting off escalating attacks from the other candidates, especially Newt Gingrich.

Santorum needs to ditch the dirge and find a spark of optimism. The Santorum I saw in one of the debates came off as a peevish complainer, offended if another participant took too much time.

I’d gladly vote for either man rather than Barack Obama, but from where I sit the moment most favors the priorities of economic conservatives. The country is mired in a dangerous rut, with a sluggish economy, an exploding debt and an out-of-control entitlement monster. The way out must begin with a rapid pickup in growth.