As the Republican presidential field shapes up, it’s essential that Republicans not repeat the error Democrats made in 2008. In that election, Democrats’ hearts, not their heads, carried the day, and at a crucial time they selected not a sober, experienced figure but an under-qualified one with a paucity of creative ideas about solving our serious problems. He got by on the most general bromides (“Go line by line through the budget”).

Frankly, virtually all of the top Republican contenders ( Rep. Michele Bachmann, Rick Perry, Mitt Romney, Rick Santorum, Newt Gingrich) have more experience than Barack Obama did when he took office. But some of them don’t appear to have thought very hard about our big challenges or come up with concrete solutions to what ails us.

On domestic policy, supposedly his strong suit, Texas Gov. Rick Perry had this to say (or his spokesman did) in New Hampshire about Social Security:

His communications director, Ray Sullivan, said Thursday that he had “never heard” the governor suggest the program was unconstitutional. Not only that, Mr. Sullivan said, but [Perry’s book] “Fed Up!” is not meant to reflect the governor’s current views on how to fix the program. . . . Mr. Perry didn’t respond when one of the protesters inside the cafe [in Portsmouth] accused him of believing the Social Security system was unconstitutional. . . .

The campaign’s disavowal of “Fed Up!” is itself very new. On Sunday evening, at Mr. Perry’s first campaign stop in Iowa, a questioner asked the governor to talk about how he would fix the country’s rickety entitlement programs. Mr. Perry shot back: “Have you read my book, ‘Fed Up!’ Get a copy and read it.”

In the book, Mr. Perry dings politicians who don’t have the courage to take on Social Security. So what is his position now? “The governor wants to see the benefits for existing retirees and those close to Social Security be strongly protected,” Mr. Sullivan said. Beyond that, “he believes a full review and discussion of entitlement reforms need to be had, aimed at seeing that programs like Social Security and Medicare are fiscally responsible and actuarially sound.”

Has he thought about this seriously? It doesn’t sound like he yet knows what to do on a major issue. He will need to formulate specific positions on taxes, health care, entitlement reform, education and regulatory reform. It is not enough in a campaign to vaguely accuse the federal government, as Perry did, of straying beyond its “constitutional responsibilities”; he needs to tell us not only what he has done in Texas but what he will do in Washington.

In that regard he is most akin at this stage to the candidate whose ideology is the most different from his own. In the Iowa debate Jon Huntsman had this exchange with Fox moderator Bret Baier:

Baier: You intend to convene a council of business leaders to figure out what is needed to improve our economy. You have been running for president for three months now. We checked your Web site. We were unable to find a detailed plan. In the middle of an economic crisis, shouldn’t you already have a pretty detailed plan by now?

Huntsman: The plan you will find on our Web site, it is coming. We’ve been in the race only for a month and and — and a half. I intend to do what I did as governor of Utah. . . . If you want to — I’m going to do what I did as governor. It is called leadership. Looking at how the free-market system works. Creating an environment that speaks to growth. We cut taxes historically. We created the most business-friendly environment in the entire country. . . . When you look at me and ask, ‘What is that guy going to do?,’ look at what I did as governor. That is what I’m going to do and what this country needs.

But it doesn’t work that way. Social Security is a federal program. What’s he going to do about it? We are $14 trillion in debt. How is he going to reduce it? We need to overhaul the tax code. What is his plan?

Considering the serious mess we are in and the calls for Obama to quit stalling, don’t his would-be replacements need to demonstrate that they have better ideas than the incumbent has? At least they should have some ideas, right?

Not all candidates are entirely without specifics. I contacted Michele Bachmann’s campaign. On bailouts for example, her campaign provided an outline to me reiterating that she opposes “providing backdoor bailouts to favored constituencies — crony capitalism at its worst. The federal government has no business choosing winners and losers in the private economy, or using taxpayer dollars to bail out politically connected companies that are dubbed ‘too big to fail.’ ” She has a long list of bailouts (TARP, the auto industry bailout, etc.) that she opposed.

On taxes, her campaign identifies a number of specifics. She has sponsored the End Tax Uncertainty Act, which would make the Bush tax cuts permanent; repeal the alternative minimum tax and the estate, gift and generation-skipping transfer taxes; and reduce the corporate tax rate to 25 percent. In addition she supported Rep. Paul Ryan’s tax reform plan, which consolidates brackets and lowers tax rates (with a maximum of 25 percent).

She has a way to go, of course. She opposed increasing the debt ceiling but declines to specify how she would have curtailed spending to keep it under the Aug. 2 limit. She nevertheless can point to a slew of spending reform measures that she has supported including the Spending Reduction Act of 2011, the Economic Recovery and Middle-Class Tax Relief Act of 2009, the Securing America’s Future Economy (SAFE) Commission Act, the Within Our Means Budget Act of 2009 and the Legislative Line Item Veto Act of 2007.

There are questions about how this all adds up, how these cuts and caps would be achieved and how the debt ceiling could remain the same while this goes into effect. We do nevertheless have some notion about what she is up to.

Mitt Romney is expected to give a detailed speech on tax policy in the fall and to address Social Security thereafter. In the meantime, he has addressed the flat tax in general terms last week in New Hampshire, saying he generally likes a flatter tax code but is concerned that a true flat tax would adversely affect the middle class. He’s been generally supportive of the Ryan Medicare plan but hasn’t embraced it specifically. He told Sean Hannity in June: “It is not my plan. It’s not my plan. My plan is different [than] the Ryan plan but he has a great start. . . . His objectives make sense. He wants more choice for the American people; that’s good.” His Web site sets positions in general terms on health care, foreign policy and other issues. (For example, he favors block-granting Medicaid and expanding health savings accounts.)

At this stage, Perry and Huntsman are merely pointing to their state records and telling the voters, “There! Take a look.” Bachmann and Romney are further along to be sure (and they sit down for interviews and/or answer questions from the media), but shouldn’t we know more?

In an ordinary election it is generally sufficient to state generic positions and describe policy proposals in broad strokes. But this is no ordinary time. Obama’s failure stems in large part from his inability to lead with constructive, feasible and concrete plans on debt reduction, taxes, job creation, trade and entitlement reform. We still don’t know what he offered in the “grand bargain.” He still doesn’t have a Social Security reform proposal. He rejected the Simpson-Bowles tax reform plan (and everything else the debt commission came up with).

It’s a bit disturbing that anyone would seek high office with only generic, or in some cases, no ideas as to what he wants to do once in office. Here’s a suggestion: By the fall debates the candidates better have thought things through and have some definite proposals on the major issues. If not, voters will conclude they aren’t any better prepared to tackle America’s big problems than the incumbent.